Polyimide precursor, resin composition comprising the polyimide precursor, pattern forming method using the resin composition, and articles produced by using the resin composition

ABSTRACT

It is a main object of the present invention to provide a polyimide precursor and a polyimide precursor resin composition, which precursor being easy to synthesize, available at low cost, excellent in storage and capable of giving polyimide that is low in impurities after imidization, irrespective of the chemical structure of the finally-obtained polyimide. 
     It is another object of the present invention to provide a polyimide precursor having repeating units represented by the following formula (1) and a photosensitive resin composition comprising the polyimide precursor and a photoacid generator or photobase generator: 
     
       
         
         
             
             
         
       
     
     In the formula (1), R 1  is a tetravalent organic group; R 2  is a divalent organic group; R 1 s may be the same or different from each other and R 2 s may be the same or different from each other in the repeating units; R 3  and R 4  respectively represent a monovalent organic group having a structure represented by the following formula (2) and may be the same or different from each other; and R 3 s and R 4 s in the repeating units may be the same or different from each other, respectively. In the formula (2), R 5 , R 6  and R 7  respectively represent a hydrogen atom, a halogen atom or a monovalent organic group; R 8  is a monovalent organic group; R 8 s in the repeating units may be the same or different from each other;  35  mole % or less of R 8 s are organic groups having a reactive group; and R 5 , R 6 , R 7  and R 8  may be bonded to each other to form a ring structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polyimide precursor, a resincomposition comprising the polyimide precursor, a pattern forming methodusing the resin composition, and articles produced by using the resincomposition.

2. Description of the Related Art

Polyimides are polymers synthesized from diamines and acid dianhydrides.Diamines react with acid dianhydrides in solvent to produce polyamicacids, which are precursors of polyimides and give polyimides throughdehydration and ring-closure reaction. In general, since polyimides havepoor solubility in solvents and are difficult to process, they are oftenobtained by making their precursors, which are polyamic acids, into adesired form followed by heating. However, polyimide precursors areoften sensitive to heat or water and thus inferior in storage stability(J. A. Kreuz, “J Polym. Sci. Part A: Polym. Chem.” vol. 28, 1990, p.3787). It is known that polyimide precursors (polyamic acids) aregenerally liable to be hydrolyzed at room temperature, which leads adecrease in molecular weight. This is said to result from the fact thatthe polyaddition reaction for preparing polyamic acids is an equilibriumreaction. More specifically, in a polyamic acid, cleavage of amino bondsinto acid anhydrides and amino groups and their recombination arecontinuously repeated. Acid anhydride groups thus contained in thesystem react with moisture in the same system to give a dicarboxylicacid, so that the acid anhydride groups are removed from saidequilibrium reaction system, which directs the equilibrium in thedirection to cut the amide bonds (in the direction to decrease themolecular weight of the polyamic acid). An improved polyimide wasdeveloped in consideration of this point, in which a skeleton excellentin solubility is introduced to a molecular structure thereof so that thepolyimide can be easily dissolved in a solvent and formed or applied.However, such a polyimide tends to be inferior in chemical resistance oradhesion to a substrate to the polyimide obtained by the method using aprecursor.

Further, a polyimide precursor has been proposed in which carboxylgroups of a polyamic acid are esterified in terms of storage stability(Japanese Patent Application Laid-Open (JP-A) No. Sho. 61-293204).However, this polyamic ester is disadvantageous in that it needs atwo-step reaction, purification for removing a condensing agent, andhigh production costs. In addition, ester bonds are hard to be thermallydecomposed; therefore, even after the polyimide precursor is imidized byheat treatment at 300° C. or more to give a polyimide, a thermaldecomposition residue derived from ester portions remains in thepolyimide, which is responsible for deterioration of properties of thepolyimide such as linear thermal expansion coefficient and humidityexpansion coefficient.

JP-A Nos. 2002-121382 and 2001-194784 have proposed negative-workingphotosensitive polyimides produced by the combination of a photoradicalgenerator and a reaction product of a vinyl ether containingphotoreactive groups with a polyamic acid. In these inventions, however,since a pattern is formed by cross-linking reaction, the molecularweight of photoreactive portions is increased and decomposed products ofthe photoreactive portions are likely to remain after imidization.Therefore, these inventions are disadvantageous in that components otherthan the polyimide remain in a film after imidization, which areresponsible for outgassing, etc. Furthermore, they are stilldisadvantageous in the following respects: gelation is likely to occurupon synthesis and/or during storage because the polyimide containslarge amounts of cross-linking components; and portions derived from thevinyl ether is eliminated from the polyamic acid over time, which leadsto a decrease in pattern forming ability, because a photoradicalgenerator and a compound containing amino groups, which is a sensitizerof the photoradical generator, are added to the polyamic acid.

JP-A No. 2005-115249 has disclosed a resin composition containing apolyimide precursor in which phenolic hydroxyl groups are eachintroduced into a carboxyl group of a polyamic acid by an ester bond, adivinyl ether compound having two vinyl ether portions and a thermallydecomposable linking group, and a photoacid generator. In the process offorming a film of the resin composition, heat applied to form a filmcauses a reaction between the phenolic hydroxyl groups and vinyl ethersto form acetal bonds, thereby cross-linking the polyimide precursor.Then, the film is exposed to generate an acid, heated to break theacetal bonds in the exposed portion only, and developed with a basicaqueous solution, thereby obtaining a positive pattern. However, JP-ANo. 2005-115249 is disadvantageous in the following respects: it isnecessary to add a polymer having a plurality of vinyl ether groups as across-linking agent, in a proportion of about 25% based on the wholepolyimide precursor; a complicated synthesis process is necessary tointroduce phenolic hydroxyl groups into a polyamic acid; and thepolyimide precursor is reacted with a vinyl ether to form a film, sothat the shape of a pattern, etc., is significantly affected by filmforming conditions or the like and thus is susceptible to changes in theprocess.

SUMMARY OF THE INVENTION

The present invention was made in the light of the circumstances asdescribed above, and it is an object of the present invention to providea polyimide precursor and a polyimide precursor resin composition, whichprecursor being easy to synthesize, available at low cost, excellent instorage and capable of giving a polyimide that is low in residualimpurities after imidization, irrespective of the chemical structure ofthe finally-obtained polyimide.

Another object of the present invention is to provide a photosensitiveresin composition which is capable of achieving a large dissolutioncontrast irrespective of the chemical structure of the finally-obtainedpolyimide and capable of achieving a pattern with excellent shape whilekeeping a sufficient process margin.

The polyimide precursor of the present invention has repeating unitsrepresented by the following formula (1):

wherein R¹ is a tetravalent organic group; R² is a divalent organicgroup; R¹s may be the same or different from each other and R²s may bethe same or different from each other in the repeating units; R³ and R⁴each independently represent a monovalent organic group having astructure represented by the following formula (2) and may be the sameor different from each other; and R³s may be the same or different fromeach other and R⁴s may be the same or different from each other in therepeating units:

wherein R⁵, R⁶ and R⁷ each independently represent a hydrogen atom, ahalogen atom or a monovalent organic group; R⁸ is a monovalent organicgroup; R⁸s may be the same or different from each other in the repeatingunits; 35 mole % or less of R₈s are organic groups having a reactivegroup; and R⁵, R⁶, R⁷ and R⁸ may be bonded to each other to form a ringstructure.

The polyimide precursor resin composition of the present inventioncomprises the polyimide precursor of the present invention and a vinylether compound.

Further, the photosensitive resin composition of the present inventioncomprises the polyimide precursor of the present invention and aphotoacid generator or comprises the polyimide precursor of the presentinvention and a photobase generator.

The present invention also provides a pattern forming method comprisingan exposure step of irradiating a surface of a film or molded body ofthe photosensitive resin composition of the present invention withelectromagnetic waves in a predetermined pattern, and a developing stepof developing either an exposed or unexposed portion with a solventwhich is capable of dissolving the exposed or unexposed portion as adeveloper.

The present invention also provides an article selected from the groupconsisting of a printed product, a display device, a semiconductordevice, electronic parts, an optical member and a building material, atleast a part of which article is formed of the polyimide resincomposition of the present invention or a cured product thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a graph showing a relationship between heating temperature andprotection rate of each polyimide precursor;

FIG. 2 is a graph plotting a peak intensity of 1,120 cm⁻¹ derived froman acetal part against temperature;

FIG. 3 is a graph showing a relationship between heating temperature andprotection rate of each polyimide precursor;

FIG. 4 is a graph showing a relationship between heating temperature andprotection rate of each polyimide precursor;

FIG. 5 is a graph showing a relationship between heating temperature andprotection rate of a film made of polyimide precursor 4;

FIG. 6 is a graph showing a relationship between heating temperature andprotection rate of a film made of polyimide precursor 8;

FIG. 7 is a microscope image of a pattern after development formed withphotosensitive resin composition 1;

FIG. 8 is a microscope image of a pattern after development formed withphotosensitive resin composition 2;

FIG. 9 is a microscope image of a pattern after development formed withphotosensitive resin composition 3;

FIG. 10 is a graph showing a relationship between heating temperatureafter exposure and dissolution rate of an exposed portion and anunexposed portion of each of films made of photosensitive resincompositions 3 to 5;

FIG. 11 is a microscope image of a pattern (negative image) afterdevelopment formed with photosensitive resin composition 5;

FIG. 12 a microscope image of a pattern (positive image) afterdevelopment formed with photosensitive resin composition 5;

FIG. 13 is a sensitivity curve of a film made of photosensitive resincomposition 6; and

FIG. 14 is microscope images of photosensitive resin composition 6 afterdevelopment and before/after imidization.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention was made by diligent studies conducted by theinventor who conceived that it would be possible to produce a polyimidewhich is capable of forming a film containing no residue derived from acarboxyl group-protecting component, by imparting storage stability byhemiacetal esterification of carboxyl groups in a polyamic acid and if,in the course of heating involved in imidization, hemiacetal ester bondsare thermally decomposed to get back into a polyamic acid and thecarboxyl group-protecting component is volatilized.

Aromatic hemiacetal ester bonds obtained from a vinyl ether can bedecomposed into a polyamic acid and a vinyl ether or acetaldehyde,alcohol, etc., by heating at 180° C. or less. The compounds produced bythermal decomposition of hemiacetal ester bonds are often liquid at roomtemperature and have a boiling point of 180° C. or less, so that a largeportion of each component volatilizes in the course of heating. In manyof polyimide precursors, imidization is generally said to proceed byheating and gradually from a temperature of around 140° C., and theglass transition temperature (Tg) of a film increases along with anincrease in the rate of imidization. Vibration of molecular chains issuppressed by the increase in Tg, so that it becomes difficult formaterials to volatilize from the inside of the film. In the case ofhemiacetal ester bonds, however, decomposition of the bonds sometimestakes place at or near room temperature, so that decomposition reactionoccurs when the imidization rate is low. Therefore, a combination ofhemiacetal ester bonds with a polyimide precursor is characterized bythat decomposed components have excellent volatility and, in the courseof heating the polyimide precursor to obtain a polyimide, decomposedcomponents are volatilized and almost no decomposed product derived fromthe hemiacetal ester bonding moieties is left in a polyimide film.Because of this, almost no residue derived from the vinyl ether is leftin the finally-obtained polyimide film, thereby achieving a film whichis very close to a pure polyimide film.

Among protecting moieties R⁸s, organic groups having a reactive groupare 35 mole % or less. This is preferred because it is possible toprevent a polyimide precursor from gelation upon synthesis or duringstorage and to reduce the amount of residues in a film.

Said polyimide precursor can be obtained simply by mixing a polyamicacid with a vinyl ether compound and stirring the mixture at roomtemperature, so that it is available at low cost and very easy toobtain. The reaction between an aromatic carboxylic acid and a vinylether compound is somewhat different in behavior from the reactionbetween an aliphatic carboxylic acid and a vinyl ether compound. Thereaction between an aliphatic carboxylic acid and a vinyl ether compoundoften needs heating or an acid catalyst; however, as a result ofdiligent studies by the inventor of the present invention, it ispossible to cause the reaction only by stirring an aliphatic carboxylicacid and a vinyl ether compound at room temperature. Furthermore, theinventor succeeded in remarkably improving the yield of reaction betweena polyamic acid and a vinyl ether compound by using a solvent containingno nitrogen atom at the time of said stirring and also by controllingthe reaction temperature. Therefore, the inventor of the presentinvention has made it possible to completely change the carboxyl groupsin an polyamic acid into hemiacetal ester bonds.

It is often the case that polyamic acids, especially aromatic polyamicacids, are dissolved in amide-based highly polar solvents because oftheir poor solubility. Amide-based solvents, however, have a problemwith handling because they have poor volatility and high waterabsorption. When a highly-concentrated polyamic acid solution absorbswater, a decrease in solubility of the polyamic acid occurs, which leadsto precipitation of the polyamic acid.

In contrast with this, the polyimide precursor of the present inventionis soluble in relatively less polar solvent because the carboxyl groupsare protected by hemiacetal ester bonds. Especially, the polyimideprecursor of the present invention shows improved solubility in solventscontaining ester bonds. Therefore, the polyimide precursor of thepresent invention also makes it possible to prepare ahighly-concentrated solution for forming a coating film.

I. Polyimide Precursor

The polyimide precursor of the present invention has repeating unitsrepresented by the following formula (1):

wherein R¹ is a tetravalent organic group; R² is a divalent organicgroup; R¹s may be the same or different from each other and R²s may bethe same or different from each other in the repeating units; R³ and R⁴each independently represent a monovalent organic group having astructure represented by the following formula (2) and may be the sameor different from each other; and R³s may be the same or different fromeach other and R⁴s may be the same or different from each other in therepeating units:

wherein R⁵, R⁶ and R⁷ each independently represent a hydrogen atom, ahalogen atom or a monovalent organic group; R⁸ is a monovalent organicgroup; R⁸s may be the same or different from each other in the repeatingunits; 35 mole % or less of R₈s are organic groups having a reactivegroup; and R⁵, R⁶, R⁷ and R⁸ may be bonded to each other to form a ringstructure.

In the formula (1), generally, R¹ has a tetracarboxylicdianhydride-derived structure and R² has a diamine-derived structure.

Examples of dianhydrides that may be used in the polyimide precursor ofthe present invention include ethylenetetracarboxylic dianhydride,butanetetracarboxylic dianhydride, cyclobutanetetracarboxylicdianhydride, cyclopentanetetracarboxylic dianhydride, pyromelliticdianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride,2,2′,3,3′-benzophenonetetracarboxylic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,2′,3,3′-biphenyltetracarboxylic dianhydride,2,2′,6,6′-biphenyltetracarboxylic dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,2,2-bis(2,3-dicarboxyphenyl)propane dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride,bis(3,4-dicarboxyphenyl)sulfone dianhydride,1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride,bis(2,3-dicarboxyphenyl)methane dianhydride,bis(3,4-dicarboxyphenyl)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,1,3-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride,1,4-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride,2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride,2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride,bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride,bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride,4,4′-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride,4,4′-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride,bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride,bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride,bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride,bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride,bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride,bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride,2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride,2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-propanedianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride,1,4,5,8-naphthalenetetracarboxylic dianhydride,1,2,5,6-naphthalenetetracarboxylic dianhydride,1,2,3,4-benzenetetracarboxylic dianhydride,3,4,9,10-perylenetetracarboxylic dianhydride,2,3,6,7-anthracenetetracarboxylic dianhydride,1,2,7,8-phenanthreneteracarboxylic dianhydride, etc.

These examples may be used solely or as a mixture of two or more kinds.

In terms of the heat resistance or linear thermal expansion coefficientof the finally-obtained polyimide film, or in terms of the reactivity ofprotecting reaction to the precursor preferably used tetracarboxylicdianhydrides are aromatic tetracarboxylic dianhydrides. Particularlypreferred tetracarboxylic dianhydrides are pyromellitic dianhydride,mellophanic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylicdianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride,2,3,2′,3′-biphenyltetracarboxylic dianhydride,2,2′,6,6′-biphenyltetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride,2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,and bis(3,4-dicarboxyphenyl)ether dianhydride.

Especially, in terms of the stability of the hemiacetal ester bonds,3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride,2,3,2′,3′-biphenyltetracarboxylic dianhydride, andbis(3,4-dicarboxyphenyl)ether dianhydride are particularly preferred.

Transparency of the polyimide precursor is increased when an aciddianhydride into which a fluorine is introduced or an acid dianhydridehaving an alicyclic skeleton structure is used as the concurrent aciddianhydride. Further, the use of a rigid acid dianhydride such aspyromellitic dianhydride, mellophanic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride,2,3,2′,3′-biphenyltetracarboxylic dianhydride, and1,4,5,8-naphthalenetetracarboxylic dianhydride, is preferred because thelinear thermal expansion coefficient of the finally-obtained polyimidebecomes smaller. Especially, in terms of the stability of the hemiacetalester bonds, particularly preferred are3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride, and2,3,2′,3′-biphenyltetracarboxylic dianhydride.

The polyimide precursor is imparted with improved transparency whenhaving an alicyclic skeleton structure as the acid dianhydride, so thatthe polyimide precursor can give a photosensitive resin compositionhaving high sensitivity. Further, heating or a catalyst is sometimesrequired for the reaction for forming hemiacetal ester bonds. In thiscase, it is possible to form hemiacetal ester bonds with relatively highstability, so that this case is preferred when priority is given tostorage stability.

On the other hand, the use of an aromatic tetracarboxylic dianhydrideenables the polyimide precursor to give a photosensitive resincomposition having excellent heat resistance and low linear thermalexpansion coefficient. Moreover, since the reaction for forminghemiacetal ester bonds proceeds at room temperature, it is very easy toobtain the intended polyimide precursor. In addition, there is anadvantage that since hemiacetal ester bonds decompose at lowertemperature, decomposed products are unlikely to remain in a film afterimidization. Therefore, in the photosensitive resin composition of thepresent invention, it is preferred that in the polyimide precursorhaving the repeating units represented by the formula (1), 33 mole % ormore of all R¹s have any of the structures represented by the followingformula (3):

Polyamic acids having the above structures are not only polyimideprecursors having high heat resistance and low linear thermal expansioncoefficient, but they are also capable of producing hemiacetal esterbonds by the reaction with a vinyl ether compound at room temperaturebecause they contain aromatic carboxylic acids. Moreover, compared tohemiacetal ester bonds obtained from aliphatic carboxylic acids,hemiacetal ester bonds obtained from the above aromatic carboxylic acidscan be thermally decomposed by heating at lower temperature, so thatthey can be decomposed more quickly by heating upon imidization and theamount of vinyl ether-derived decomposed products in thefinally-obtained polyimide is small. Therefore, it becomes easier toachieve the objects of the present invention if, among all R¹s in therepeating units represented by the formula (1), the content of R¹shaving any of the structures represented by the formula (3) is closer to100 mole %. Nevertheless, it is still possible to achieve the objects ifthe content is at least 33 mole % or more. More specifically, among allR¹s in the repeating units represented by the formula (1), the contentof R¹s having any of the structures represented by the formula (3) ispreferably 50 mole % or more, and more preferably 70 mole % or more.

On the other hand, as the diamine component that may be used to producethe polyimide precursor of the present invention, it is possible to useone kind of diamine alone or two kinds of diamines in combination. Noparticular limitation is imposed on the diamine component used herein,and there may be used p-phenylenediamine, m-phenylenediamine,o-phenylenediamine, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenylether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfide,3,4′-diaminodiphenyl sulfide, 4,4′-diaminodiphenyl sulfide,3,3′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone,4,4′-diaminodiphenyl sulfone, 3,3′-diaminobenzophenone,4,4′-diaminobenzophenone, 3,4′-diaminobenzophenone,3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane,3,4′-diaminodiphenylmethane, 2,2-di(3-aminophenyl)propane,2,2-di(4-aminophenyl)propane,2-(3-aminophenyl)-2-(4-aminophenyl)propane,2,2-di(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane,2,2-di(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane,2-(3-aminophenyl)-2-(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane,1,1-di(3-aminophenyl)-1-phenylethane,1,1-di(4-aminophenyl)-1-phenylethane,1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane,1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene,1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene,1,4-bis(3-aminobenzoyl)benzene, 1,4-bis(4-aminobenzoyl)benzene,1,3-bis(3-amino-α,α-dimethylbenzyl)benzene,1,3-bis(4-amino-α,α-dimethylbenzyl)benzene,1,4-bis(3-amino-α,α-dimethylbenzyl)benzene,1,4-bis(4-amino-α,α-dimethylbenzyl)benzene,1,3-bis(3-amino-α,α-ditrifluoromethylbenzyl)benzene,1,3-bis(4-amino-α,α-ditrifluoromethylbenzyl)benzene,1,4-bis(3-amino-α,α-ditrifluoromethylbenzyl)benzene,1,4-bis(4-amino-α,α-ditrifluoromethylbenzyl)benzene,2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine,4,4′-bis(3-aminophenoxy)biphenyl, 4,4′-bis(4-aminophenoxy)biphenyl,bis[4-(3-aminophenoxy)phenyl]ketone,bis[4-(4-aminophenoxy)phenyl]ketone,bis[4-(3-aminophenoxy)phenyl]sulfide,bis[4-(4-aminophenoxy)phenyl]sulfide,bis[4-(3-aminophenoxy)phenyl]sulfone,bis[4-(4-aminophenoxy)phenyl]sulfone,bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether,2,2-bis[4-(3-aminophenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane,2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane,1,3-bis[4-(3-aminophenoxy)benzoyl]benzene,1,3-bis[4-(4-aminophenoxy)benzoyl]benzene,1,4-bis[4-(3-aminophenoxy)benzoyl]benzene,1,4-bis[4-(4-aminophenoxy)benzoyl]benzene,1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene,1,3-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene,1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene,1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene,4,4′-bis[4-(4-aminophenoxy)benzoyl]diphenylether,4,4′-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone,4,4′-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenylsulfone,4,4′-bis[4-(4-aminophenoxy)phenoxy]diphenylsulfone,3,3′-diamino-4,4′-diphenoxybenzophenone,3,3′-diamino-4,4′-dibiphenoxybenzophenone,3,3′-diamino-4-phenoxybenzophenone,3,3′-diamino-4-biphenoxybenzophenone,6,6′-bis(3-aminophenoxy)-3,3,3′,3′-tetramethyl-1,1′-spirobiindan,6,6′-bis(4-aminophenoxy)-3,3,3′,3′-tetramethyl-1,1′-spirobiindan,1,3-bis(3-aminopropyl)tetramethyldisiloxane,1,3-bis(4-aminobutyl)tetramethyldisiloxane,α,ω-bis(3-aminopropyl)polydimethylsiloxane,α,ω-bis(3-aminobutyl)polydimethylsiloxane, bis(aminomethyl)ether,bis(2-aminoethyl)ether, bis(3-aminopropyl)ether,bis(2-aminomethoxy)ethyl]ether, bis[2-(2-aminoethoxyl)ethyl]ether,bis[2-(3-aminopropoxy)ethyl]ether, 1,2-bis(aminomethoxy)ethane,1,2-bis(2-aminoethoxyl)ethane, 1,2-bis[2-(aminomethoxy)ethoxy]ethane,1,2-bis[2-(2-aminoethoxyl)ethoxy]ethane, ethylene glycolbis(3-aminopropyl)ether, diethylene glycol bis(3-aminopropyl)ether,triethylene glycol bis(3-aminopropyl)ether, ethylenediamine,1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane,1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane,1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane,1,12-diaminododecane, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane,1,4-diaminocyclohexane, 1,2-di(2-aminoethyl)cyclohexane,1,3-di(2-aminoethyl)cyclohexane, 1,4-di(2-aminoethyl)cyclohexane,bis(4-aminocyclohexyl)methane,2,6-bis(aminomethyl)bicyclo[2.2.1]heptane,2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, and the above diamines inwhich some or all of the hydrogen atoms of aromatic rings aresubstituted with substituents selected from the group consisting offluoro groups, methyl groups, methoxy groups, trifluoromethyl groups andtrifluoromethoxy groups.

Furthermore, depending on the intended purpose, there may be used theabove diamines in which some or all of the hydrogen atoms of aromaticrings are substituted with one or more kinds of substituents selectedfrom the group consisting of ethynyl groups, benzocyclobutene-4′-ylgroups, vinyl groups, allyl groups, cyano groups, isocyanate groups andisopropenyl groups, all of which groups act as cross-linking sites.

In the present invention, it is possible to select a diamine dependingon desired physical properties. The use of a rigid diamine such asp-phenylenediamine imparts a low expansion coefficient to thefinally-obtained polyimide. A diamine in which two amino groups arebonded to one aromatic ring is a rigid diamine, and examples of such adiamine include p-phenylenediamine, m-phenylenediamine,1,4-diaminonaphthalene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene,2,7-diaminonaphthalene, and 1,4-diaminoanthracene.

Further, there may be used a diamine in which two or more aromatic ringsare bonded to each other by a single bond, and two or more amino groupsare respectively and independently bonded to a different aromatic ringdirectly or as a part of substituent. Such a diamine is, for example,one represented by the following formula (5) and a specific examplethereof is benzidine.

In the formula (5), “a” is a natural number of 1 or more; each of theamino groups is bonded in the meta- or para-position relative to thebond connecting the benzene rings; and R¹³ and R¹⁴ are a monovalentorganic group or a halogen atom.

Furthermore, there may be used a diamine as shown in the formula (5),which has substituents at certain positions of the benzene rings, whichpositions are not involved in bonding to other benzene rings andsubstituted by amino groups. These substituents are monovalent groupsand may be bonded to each other.

Specific examples of such a diamine include2,2′-dimethyl-4,4′-diaminobiphenyl,2,2′-ditrifluoromethyl-4,4′-diaminobiphenyl,3,3′-dichloro-4,4′-diaminobiphenyl, 3,3′-dimethoxy-4,4′-diaminobiphenyl,and 3,3′-dimethyl-4,4′-diaminobiphenyl.

A fluorine may be introduced as a substituent of the aromatic ring ifthe finally-obtained polyimide is intended to be used as an opticalwaveguide or optical circuit part, so that the finally-obtainedpolyimide can be imparted with improved transmittance with respect toelectromagnetic waves having a wavelength of 1 μm or less.

On the other hand, the use of a diamine having a siloxane skeleton, suchas 1,3-bis(3-aminopropyl)tetramethyldisiloxane, can decrease the elasticmodulus and thus glass transition temperature of the finally-obtainedpolyimide.

It is to be noted that the diamine selected herein is preferably anaromatic diamine; however, a non-aromatic diamine such as an aliphaticdiamine and a siloxane diamine may be selected depending on a desiredphysical property, insofar as the amount of the non-aromatic diaminedoes not exceed 60 mole %, preferably 40 mole % of the whole diamine.

Further, it is preferred that in the polyimide precursor, 33 mole % ormore of R²s in the repeating units represented by the formula (1) hasany of the structures represented by the following formula (4):

wherein R¹⁰ is a divalent organic group, an oxygen atom, a sulfur atomor a sulfonic group; and R¹¹ and R¹² are a monovalent organic group or ahalogen atom.

Increased heat resistance is imparted to the finally-obtained polyimidewhen any of the above structures is contained in the polyimideprecursor. Therefore, it becomes easier to achieve the objects of thepresent invention if, among the R²s in the repeating units representedby the formula (1), the content of R²s having any of the structuresrepresented by the formula (4) is closer to 100 mole %. Nevertheless, itis still possible to achieve the objects if the content is at least 33mole % or more. More specifically, among all R²s in the repeating unitsrepresented by the formula (1), the content of R²s having any of thestructures represented by the formula (4) is preferably 50 mole % ormore, and more preferably 70 mole % or more.

In the formula (1), R³ and R⁴ each independently represent a monovalentorganic group having a structure represented by the following formula(2) and may be the same or different from each other; and R³s may be thesame or different from each other and R⁴s may be the same or differentfrom each other in the repeating units:

The hemiacetal ester bonds represented by the formula (2) can beobtained by the following reaction of a carboxyl group with a vinylether compound, for example:

More specifically, in the case of forming the hemiacetal ester bonds bythe addition reaction of a carboxylic acid with a vinyl ether compound,R⁵, R⁶, R⁷ and R⁸ in the formula (2) are determined by the structure ofthe vinyl ether compound used. The structure represented by the formula(2) may be formed with a cyclic vinyl ether compound such asdihydropyran. In this case, despite poor reactivity and a long reactiontime, a polyimide precursor having high heat resistance and excellentthermal stability can be obtained. For a shorter reaction time andimproved productivity, it is preferred to use an acyclic vinyl ethercompound. It is to be noted that the cyclic vinyl ether is, like3,4-dihydro-2H-pyran, a vinyl ether having a vinyl bond whichconstitutes a part of the cyclic structure thereof. For example, despitehaving a cyclic structure, cyclohexyl vinyl ether and2-vinyloxytetrahydropyran are classified into acyclic vinyl ethersbecause a vinyl group thereof does not constitute a part of the cyclicstructure. The structure represented by the formula (2) is the portionintended by the present invention to be connected to and then eliminatedfrom the main chain of the polyimide precursor by a hemiacetal esterbond. Accordingly, the structure represented by the formula (2)preferably has a low molecular weight and become highly volatile afterdecomposition, so that it is possible to reduce the amount of decomposedproducts remaining in the finally-obtained polyimide film.

In terms of material availability, R⁵, R⁶ and R⁷ are preferably ahydrogen atom, a substituted or unsubstituted alkyl group, allyl group,or aryl group. Among them, a hydrogen atom is particularly preferred. Inaddition, it is preferred that R⁵, R⁶ and R⁷ contain no substituenthaving an active hydrogen, such as a primary, secondary or tertiaryamino group and a hydroxyl group.

This substituent having an active hydrogen refers to a substituentcapable of exchange reaction with the hemiacetal ester bond. Specificexamples of the substituent include a hydroxyl group, a primary aminogroup, a secondary amino group, a tertiary amino group, a carboxyl groupand a mercapto group, according to “Kagaku Jiten” (Dictionary ofChemistry) published by Tokyo Kagaku Dozin Co., Ltd.

R⁸ in the formula (2) is a monovalent organic group having one or morecarbon atoms. Examples of R⁸ include groups having a hydrocarbonskeleton. They may also contain a bond or substituent other than ahydrocarbon, such as a hetero atom, and the hetero atom part may beincorporated into an aromatic ring to form a heterocyclic ring. Examplesof the group having a hydrocarbon skeleton include a straight-chain,branched-chain or alicyclic saturated or unsaturated hydrocarbon group;a straight- or branched-chain saturated or unsaturated halogenated alkylgroup; an aromatic group such as a phenyl or a naphthyl; a group inwhich an ether bond is contained in a straight- or branched-chainsaturated or unsaturated hydrocarbon skeleton (for example,—(R—O)_(n)—R′ wherein R and R′ is a substituted or unsubstitutedsaturated or unsaturated hydrocarbon, and n is an integer of 1 or more;and —R″—(O—R′″)_(m) wherein R″ and R′″ is a substituted or unsubstitutedsaturated or unsaturated hydrocarbon, m is an integer of 1 or more, and—(O—R′″)_(m) is bonded to a carbon which is different from a terminal ofR″); a group in which a thioether bond is contained in a straight- orbranched-chain saturated or unsaturated hydrocarbon skeleton; andvarious groups comprising a straight- or branched-chain saturated orunsaturated hydrocarbon skeleton to which a hetero atom or a heteroatom-containing group is bonded, examples of which hetero atom andhetero atom-containing group include a halogen atom, a cyano group, asilyl group, a nitro group, an acetyl group, an acetoxy group and asulfone group. Further, R⁸ in the formula (2) may be connected to R⁵ orR⁶ to form a ring structure.

When a substituent having an active hydrogen such as a primary,secondary or tertiary amino group or a hydroxyl group is contained, thehemiacetal ester bonds become more decomposable and the storagestability of the polyimide precursor is thus decreased. For this reason,it is preferred that R⁸ in the formula (2) contain no active hydrogen.

Furthermore, the polyimide precursor tends to have poor storagestability when R⁸ in the formula (2) contains a reactive group such as areactive ethylenic unsaturated bond. For this reason, even in the casewhere reactive unsaturated bonds are contained, the content ispreferably small; moreover, the repeating units in which a reactivegroup is contained in R⁸ in the formula (2) account for 35 mole % orless of all the repeating units represented by the formula (1). It ispreferred that R⁸ in the formula (2) contain substantially no reactivegroup so as to make decomposed products of R⁸s produced after cuttingthe hemiacetal bonds less likely to remain in the finally-obtainedpolyimide film. Examples of the reactive group include a glycidyl group,an oxetanyl group and an isocyanuric group, in addition to an ethylenicunsaturated bond.

Especially from the viewpoint of adhesion to a substrate, storagestability, resistance to repellent and volatility of decomposedproducts, R⁸ in the formula (2) preferably contains an ether bond in thehydrocarbon skeleton. R⁸ may also contain a polyoxyalkylene skeleton.When a polyoxyalkylene skeleton is contained, the number of repeatedoxyalkylenes is preferably 15 or less in terms of volatility ofdecomposed products.

Hemiacetal ester bonds are decomposed into a carboxylic acid and otherproducts by heating. Generally, the decomposition temperature increasesin the following order of carbon atoms which are each bonded at R⁸ inthe formula (2) to the oxygen atom of the ether bond: a tertiary carbonatom (hereinafter it may be simply referred to as “tertiary carbon”)<asecondary carbon atom (hereinafter it may be simply referred to as“secondary carbon”)<a primary carbon atom (hereinafter it may be simplyreferred to as “primary carbon”).

On the other hand, in the reaction between a vinyl ether compound and acarboxylic acid for obtaining a hemiacetal ester bond, the reactivitygenerally increases in the following order of carbon atoms which areeach bonded at R⁸ in the formula (2) to the oxygen atom: a primarycarbon<a secondary carbon<a tertiary carbon.

In the present invention, it is to be noted that a primary carbon atomis one that is attached to zero or one other carbon atom; a secondarycarbon atom is one that is attached to two other carbon atoms; atertiary carbon atom is one that is attached to three other carbonatoms, regarding the carbon atom which is a constituent of thehemiacetal ester bond and bonded to an ether oxygen atom (the carbonatom bonded at R⁸ in the formula (2) to the oxygen atom) or the othercarbon atom which is bonded to an ether oxygen atombonded to a vinylgroup of the vinyl ether compound, which vinyl group derives thehemiacetal ester bond.

Consequently, when the carbon bonded at R⁸ in the formula (2) to theoxygen atom is a primary carbon, the polyimide precursor is impartedwith high stability and can be stored for a longer time. Additionally,the heating temperature in the process of, for example, forming a filmcan be set higher, which makes the polyimide precursor more stable inthe process.

When the carbon bonded at R⁸ in the formula (2) to the oxygen atom is atertiary carbon, the polyimide precursor becomes slightly unstable;however, it is possible to the decompose hemiacetal ester bond byheating at a lower temperature. Therefore, decomposition of thehemiacetal ester bonds and volatilization of decomposed products proceedmore smoothly in the heating process for imidization, and it is possibleto reduce the amount of residual components of protective group-deriveddecomposed products in the finally-obtained polyimide film by heatingfor a shorter period. In most cases, the amount can be reduced tosubstantially zero. The carbon which is bonded at R⁸ in the formula (2)to the oxygen atom is preferably a tertiary carbon if it is required toobtain the polyimide precursor containing hemiacetal ester bonds in ashort reaction time.

When the carbon bonded at R⁸ in the formula (2) to the oxygen atom is asecondary carbon, it is possible to obtain a photosensitive resincomposition which is intermediate in properties between the case of aprimary carbon and that of a tertiary carbon, and well-balanced betweenstorage stability of the polyimide precursor, eliminatability of theprotective groups and reactivity to the hemiacetal ester bond.

In terms of volatility of the decomposed products, R⁸ in the formula (2)preferably has 1 to 30 carbon atoms, more preferably 2 to 15 carbonatoms.

In the structure of R⁸ in the formula (2), R⁸ is preferably a monovalentC2-C30 organic group containing an ether bond. More preferably, R⁸ is amonovalent C2-C30 organic group containing an ether bond and notcontaining an active hydrogen.

No particular limitation is imposed on R⁸ in the formula (2). Examplesof R⁸ include a methyl group, an ethyl group, an ethynyl group, a propylgroup, an isopropyl group, an n-butyl group, a t-butyl group, an n-hexylgroup, a cyclohexyl group, a cyclohexylmethyl group, a methoxyethylgroup, an ethoxyethyl group, a propoxyethyl group, a butoxyethyl group,a cyclohexyloxyethyl group, a methoxypropyl group, an ethoxypropylgroup, a propoxypropyl group, a butoxypropyl group, acyclohexyloxypropyl group, and a 2-tetrahydropyranyl group.Additionally, examples of R⁸ include a ring structure in which R⁸ in theformula (2) is connected to R⁵ or R⁶, thereby allowing a substituentcorresponding to R³ and/or R⁴ to form a cyclic ether such as a2-tetrahydropyranyl group.

R⁸ in the formula (2) may be a mixture prepared by appropriatelycombining two or more kinds of protecting moieties each having differentchemical structures. As a result of this, stability upon heating oragainst an acid or basic material is varied depending on the structureof R⁸. Therefore, it becomes possible to stably control the rate ofhemiacetal ester bond decomposition by heating, an acid material or abasic material, or the rate of imidization by heating in the presence ofan acid or a base. That is, the decomposability of the hemiacetal esterbonds varies depending on the chemical structures of the protectingmoieties. Accordingly, in the case where the polyimide precursor hasvarious types of protecting moieties, it is possible to control thesolubility in a developer in stages, corresponding to the introductionrates of the protecting moieties. Therefore, the polyimide precursor canbe a material with a wide process margin.

For instance, in the case of using a protecting moiety with high heatresistance and that with low heat resistance in combination, it ispossible to selectively decompose the protecting moiety with low heatresistance only, by heating at a temperature which is lower than thedecomposition temperature of the protecting moiety with high heatresistance and which is also the same as or higher than thedecomposition temperature of the protecting moiety with low heatresistance. In other words, it is possible to selectively decompose theprotecting moiety with low heat resistance only, by heating under thecondition in which there is a large difference between the decompositionrates of the protecting moieties heated in an identical condition.Consequently, when using two or more kinds of protecting moieties incombination, that is, when R⁸ in the formula (2) contains two or morekinds of organic groups, the moieties/groups are preferably selected sothat, for example, the difference between the decomposition rates of atleast two kinds of hemiacetal ester bonds heated in an identical heatingcondition is 30% or more on the same heating condition, more preferably50% or more, and still more preferably 70% or more.

An example of said heating condition is the case where a 1 wt %deuterated DMSO solution of the polyimide precursor is heated in a NMRtube or where the solution is applied on a non-alkali glass substratehaving a thickness of 800 μm and heated on a hot plate. Thedecomposition temperature can be measured by, for example, the integralratio of two hydrogen peaks measured by NMR, the first hydrogen peakbeing derived from hemiacetal ester bonds and the second being that ofamide groups or aromatic rings, or from the integral ratio of vinylether-derived peaks observed in an IR spectrum.

As described above, in the case of using a protecting moiety with highheat resistance and a protecting moiety with low heat resistance incombination, it is possible to control the proportion of carboxyl groupsleft after heating by controlling the introduction rate of theprotecting moiety with low heat resistance. In the polyimide precursor,the proportion of carboxyl groups is an important factor in determininga dissolution rate of the precursor in a basic solution, and controllingthe proportion of carboxyl groups so as to have sufficientreproducibility makes it possible to stably obtain a pattern withexcellent shape, thereby increasing the practicality of the polyimideprecursor.

Provided that A1 refers to a group consisting of organic groups in whichthe carbon atom bonded at R⁸ in the formula (2) to the oxygen atom is aprimary carbon atom; A2 refers to a group consisting of organic groupsin which said carbon atom is a secondary carbon atom; and A3 refers to agroup of organic groups in which said carbon atom is a tertiary carbonatom, R⁸ may be a mixture comprising A1 and A2; A1 and A3; A2 and A3; orA1, A2 and A3, and the mixture containing two or more kinds of organicgroups by combining one or more kinds of each group in the abovecombination. As just described, in the case where two or more kinds oforganic groups having carbon atoms in different types of classificationare contained as R⁸, there is a relatively large difference between thereactivities of vinyl ether compounds used as raw materials or betweenthe thermal decomposition temperatures of hemiacetal ester bonds.Therefore, it is easy to realize more stable control of the introductionratios of two or more different types of hemiacetal ester bonds.Further, it is possible to realize more stable control of thedecomposition rates of hemiacetal ester bonds by heating.

In general, as described above, high stability is obtained when thecarbon bonded at R⁸ to the oxygen atom is a primary carbon (A1), and thestability decreases in the order of a secondary carbon (A2) and atertiary carbon (A3). Accordingly, by combining protecting moieties soas to have a primary carbon (A1) and a secondary carbon (A2) and/or atertiary carbon (A3), protecting moieties can be decomposed selectivelyand thus stable pattern formation is realized.

R⁸ in the formula (2) may be a combination of two or more kinds selectedfrom A1s, A2s or A3s. Such a combination may be also used to control thedecomposition rate if the structure of R⁸ is selected so as toappropriately obtain a difference between the decomposabilities ofhemiacetal bonds.

The group of organic groups A1 (A1′ and A1″) in which the carbon atombonded at R⁸ to the oxygen atom is a primary carbon atom includes, forexample, organic groups represented by the following formulae (6-1) and(6-1′). The group of organic groups A2 in which said carbon atom is asecondary carbon atom includes, for example, organic groups representedby the following formula (6-2). The group of organic groups A3 in whichsaid carbon atom is a tertiary carbon atom includes, for example,organic groups represented by the following formula (6-3).

In formulae (6-1) to (6-3), R²⁰ to R²⁵ are independently a monovalentorganic group, and X is independently a hydrogen atom, a halogen atom,an alkoxycarbonyl group, an acyloxy group, a benzoyloxy group which maycontain a substituent, an alkylthio group, a phenylthio group which maycontain a substituent, or an alkoxy group. R²⁰ and X may be bonded toeach other to form a ring structure. R²¹, R²² and X may be bonded toeach other to form a ring structure. R²³, R²⁴ and R²⁵ may be bonded toeach other to form a ring structure.

In the above formulae (6-1) to (6-3), R²⁰ to R²⁵ are independently amonovalent organic group and bonded to the carbon atom shown in theformulae (6-1) to (6-3) via a carbon atom. Examples of R²⁰ to R²⁵ aregroups having a hydrocarbon skeleton. Such groups may also contain abond or substituent other than a hydrocarbon, such as a hetero atom, andthe hetero atom may be incorporated into an aromatic ring to form aheterocyclic ring. The groups having a hydrocarbon skeleton may be thesame as those disclosed in the above description regarding A.

An example of a ring structure formed by bonding R²¹ and R²² to eachother is a cyclohexyl group. An example of a ring structure formed bybonding R²³, R²⁴ and R²⁵ to each other is an adamantyl group.

Meanwhile, in the above formulae (6-1) to (6-3), X is independently ahydrogen atom, a halogen atom, an alkoxycarbonyl group, an acyloxygroup, a benzoyloxy which may contain a substituent, an alkylthio group,a phenylthio group which may contain a substituent, or an alkoxy group.An example of a hydrocarbon group bonded to an alkoxycarbonyl group(—COOR), an acyloxy group (—OCOR) or an alkoxy group (—OR) is astraight-chain, branched-chain or alicyclic saturated or unsaturatedhydrocarbon group. The alkoxy group may be bonded to R⁸ in the formula(2) to form a cyclic ether structure so that R⁸ becomes a2-tetrahydropyranyl group.

In terms of easy availability of raw materials, X in the formulae (6-1)to (6-3) is preferably a hydrogen atom or an alkoxy group.

Also, a polyimide precursor into which protecting moieties each having adifferent chemical structures are introduced can be synthesized byallowing a vinyl ether having two or more kinds of chemical structuresto react with a polyamic acid in stages or at once.

Methods for producing the polyimide precursor of the present inventionmay be conventionally known methods. For example, it maybe, but notlimited to, a method in which a polyamide acid, which is a precursor, issynthesized from an acid dianhydride and a diamine and reacted with avinyl ether compound. Also, there may be a method in which a dicarboxydihemiacetal ester compound is prepared by reaction of a tetracarboxylicacid with two equivalents of vinyl ether compound, which is thensubjected to dehydration-condensation reaction with diamine to produce apolymer.

Said polyimide precursor is generally obtained by reaction of a polyamicacid with a vinyl ether compound. According to the studies by theinventor of the present invention, the reaction has a tendency that theyield of hemiacetal ester bonds is low in a solvent containing an activehydrogen such as an amino group or a hydroxyl group, or in the presenceof a compound containing an active hydrogen such as an amino group or ahydroxyl group. Furthermore, the same tendency is observed when using asolvent containing, in a skeleton thereof, a nitrogen atom which is inthe form other than a nitro group. In the present invention, therefore,it is not preferred to use solvents containing in their skeletons anitrogen atom which is in the form other than a nitro group.

In general, polyimides having low linear thermal expansion coefficientare aromatic polyimides. Aromatic polyamic acids are precursors of suchpolyimides and exhibit high solubility in amide solvents containing anitrogen atom such as N-methylpyrrolidone or dimethylacetamide. In mostcases, however, they exhibit low solubility in solvents containing nonitrogen atom, such as non-amide solvents. Especially, an aromaticpolyamic acid which has any of the structures represented by the formula(3) as R¹ and any of the structures represented by the formula (5) as R²respectively and thus is capable of realizing low expansioncharacteristics, is not completely soluble in non-amide solvents such aslactones and sulfoxides. It is to be noted herein that “not completelysoluble” means the state in which a polyamic acid cannot be completelydissolved at a concentration required in the reaction or to form a film,for example, at a concentration of 16.5% by weight in a solvent at 23°C.

According to the conventional technique as JP-A No. 2001-194784, anaromatic polyamic acid is reacted with a vinyl ether compound in thestate of being dissolved in an amide solvent. Therefore, by such aconventional art, it is conventionally impossible to synthesize a 100%hemiacetal-esterified polyimide precursor derived from an aromaticpolyamic acid, which has any of the structures represented by theformula (3) as R¹ and any of the structures represented by the formula(5) as R² and thus is capable of realizing low expansioncharacteristics.

In contrast, the present invention has succeeded in producing apolyimide precursor in which 100% of the carboxyl groups in a polyamicacid are changed into hemiacetal ester bonds. The polyimide precursorhaving hemiacetal ester bonds used in the present invention is impartedwith increased solubility by hemiacetal-esterifying the carboxyl groups,so that it exhibits high solubility even in a solvent containing nonitrogen atom, such as a non-amide solvent. Accordingly, an excellentreaction efficiency is obtained when said polyamic acid is reacted witha vinyl ether compound in a solvent containing no nitrogen atom.However, as described above, it is often the case that the polyamic acidwhich is capable of achieving a polyimide with low linear expansioncoefficient is not completely dissolved, initially. The polyimideprecursor of the present invention, however, is produced in such a waythat the polyimide precursor starts to dissolve in a reaction solventwith the progress of reaction of a polyamic acid with a vinyl ethercompound, and it finally dissolved completely. More specifically, in thepresent invention, it is possible to obtain the polyimide precursor byreaction in one or more kinds of solvents selected from lactones andsulfoxides between a polyamic acid which is not completely soluble inthis solvent and a vinyl ether compound.

Because it is possible to produce a polyimide precursor in which 100% ofthe carboxyl groups of a polyamic acid are changed into hemiacetal esterbonds, among solvents containing no nitrogen atom, a reaction solventselected from lactones and sulfoxides is preferably used as the reactionsolvent used in the reaction between a polyamic acid and a vinyl ether.Examples of lactones include γ-butyrolactone, α-acetyl-γ-butyrolactone,ε-caprolactone, γ-hexanolactone and δ-hexanolactone. Examples ofsulfoxides include dimethyl sulfoxide, methyl ethyl sulfoxide, anddiethyl sulfoxide. While having high solubility, dimethyl sulfoxide hasbeen found to resist oxidization and be mutagenic and thus has a problemwith stability or safety required for a solvent. Accordingly, lactonesare particularly preferred.

Because it is possible to produce a polyimide precursor in which 100% ofthe carboxyl groups in a polyamic acid are changed into hemiacetal esterbonds, the reaction temperature of the reaction between a polyamic acidand a vinyl ether is preferably 5 to 35° C., more preferably 10 to 30°C. At temperatures higher than the range, a side reaction such asdecomposition of hemiacetal ester bonds proceeds, which tends to obtainno polyimide precursor in which 100% of the carboxyl groups in apolyamic acid are changed into hemiacetal ester bonds.

The polyimide precursor used in the present invention has highsolubility in non-amide solvents having a low boiling point, therebyproviding improved handleability in the process of coating, etc.

In the present invention, the vinyl ether compound may be selectedappropriately depending on the structure of a desired hemiacetal esterbond. For instance, specific examples of primary vinyl ether compoundscapable of deriving said A1 include vinyl ether compounds having astraight- or branched-chain saturated or unsaturated hydrocarbonskeleton, such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinylether, n-butyl vinyl ether, n-amyl vinyl ether, octadecyl vinyl ether;vinyl ether compounds having an alicyclic saturated hydrocarbonskeleton, such as cyclohexyl methyl vinyl ether, tricyclodecanyl methylvinyl ether, pentacyclopentadecanyl methyl vinyl ether; and vinyl ethersin which an ether bond is contained in a straight-chain, branched-chainor alicyclic saturated or unsaturated hydrocarbon, such as ethyleneglycol methyl vinyl ether, ethylene glycol ethyl vinyl ether, ethyleneglycol propyl vinyl ether, ethylene glycol butyl vinyl ether,polyethylene glycol methyl vinyl ether, polyethylene glycol ethyl vinylether, polyethylene glycol propyl vinyl ether, polyethylene glycol butylvinyl ether, polyethylene glycol octyl vinyl ether, propylene glycolmethyl vinyl ether, propylene glycol ethyl vinyl ether, propylene glycolpropyl vinyl ether, propylene glycol butyl vinyl ether, polypropyleneglycol methyl vinyl ether, polypropylene glycol ethyl vinyl ether,polypropylene glycol propyl vinyl ether, polypropylene glycol butylvinyl ether, polypropylene glycol octyl vinyl ether, butylene glycolmethyl vinyl ether, butylene glycol ethyl vinyl ether, butylene glycolpropyl vinyl ether, butylene glycol butyl vinyl ether, polybutyleneglycol methyl vinyl ether, polybutylene glycol ethyl vinyl ether,polybutylene glycol propyl vinyl ether, polybutylene glycol butyl vinylether, polybutylene glycol octyl vinyl ether, and2-vinyloxytetrahydropyran. Additionally, said examples include cyclicvinyl ether compound such as 3,4-dihydro-2H-pyran, 2,3-dihydrofuran,3,4-dihydro-2-methoxy-2H-pyran, and 3,4-dihydro-2-ethoxy-2H-pyran.

Specific examples of secondary vinyl ether compounds capable of derivingsaid A2 include vinyl ether compounds having a straight- orbranched-chain saturated or unsaturated hydrocarbon skeleton, such asisopropyl vinyl ether, sec-butyl vinyl ether, and sec-pentyl vinylether; vinyl ether compounds having an alicyclic saturated hydrocarbonskeleton, such as cyclohexyl vinyl ether, tricyclodecanyl vinyl ether,and pentacyclopentadecanyl vinyl ether; and vinyl ethers in which anether bond is contained in a straight- or branched-chain saturated orunsaturated hydrocarbon skeleton, such as 1-methoxyethyl vinyl ether,1-ethoxyethyl vinyl ether, 1-methyl-2-methoxyethyl vinyl ether, and1-methyl-2-ethoxyethyl vinyl ether.

Specific examples of tertiary vinyl ether compounds capable of derivingsaid A3 include vinyl ether compounds having a straight- orbranched-chain saturated or unsaturated hydrocarbon skeleton, such astert-butyl vinyl ether and tert-amyl vinyl ether; vinyl ether compoundshaving an alicyclic saturated hydrocarbon skeleton, such as1-methylcyclohexyl vinyl ether and 1-adamantyl vinyl ether; and vinylethers in which an ether bond is contained in a straight- orbranched-chain saturated or unsaturated hydrocarbon skeleton, such as1,1-dimethyl-2-methoxyethyl vinyl ether.

When said primary, secondary and tertiary vinyl ether compounds containpolyoxyalkylene residues, the number of repeated oxyalkylene residues ispreferably 15 or less in terms of volatility after decomposition.

The method of producing the polyimide precursor of the present inventionmay be a novel method of producing a polyimide precursor by polymerizingone or more kinds of acid dianhydrides and one or more kinds of diaminesin a solution containing a vinyl ether compound.

Carboxylic acids, especially aromatic carboxylic acids and vinyl ethercompounds react with each other when mixed in a non-amide solvent atroom temperature, thereby forming hemiacetal ester bonds in good yield.On the other hand, polyamic acids, which are precursors of polyimideshaving a structure capable of showing high heat resistance and lowlinear thermal expansion coefficient, have poor solubility in anon-amide solvent such as γ-butyrolactone and cyclopentanone due tochemical structures thereof, and polymerization reaction cannot proceeduniformly. Therefore, it is conventionally impossible to carry outpolymerization and hemiacetal esterification of a polyamic acid in anidentical solvent system.

As a result of diligent researches, the inventor of the presentinvention has found out the aforementioned, novel production method.

The polyamic acid with poor solubility in a non-amide solvent cangradually increase its solubility in a non-amide solvent as the reactionwith a vinyl ether compound proceeds and carboxyl groups arehemiacetal-esterified. At the point when a certain percentage or more ofcarboxyl groups are hemiacetal-esterified, the polyamic acid becomesoluble in a non-amide solvent or mixed solution of a non-amide solventand a vinyl ether compound.

By using this phenomenon and polymerizing one or more kinds of aciddianhydrides and one or more kinds of diamines in the presence of avinyl ether compound, a reaction occurs between the acid dianhydridesand diamines to produce carboxyl groups, and part of the reactionproducts precipitate from the solution. However, carboxyl groups of partof the reaction products dissolved in the solvent react with the vinylether compound in the solvent to produce hemiacetal ester bonds,resulting in an increase in solubility. Then, a precipitated amic acidgradually reacts with the vinyl ether compound and gradually dissolves.After the amic acid is totally hemiacetal-esterified, all thereof cometo dissolve.

In general, low-molecular-weight polymers are often highly soluble. Thistendency is stronger when polymers including repeating units having ahighly-polar structure, such as carboxyl groups, are dissolved in asolvent of low polarity.

That is, even in the case of a chemical structure having low solubilityin non-amide solvent, the novel production method of the presentinvention can provide a hemiacetal-esterified polyimide precursorprepared in one pot by promoting a hemiacetal-esterification reactiongradually from the stage of a low-molecular-weight amic acid havingrelatively high solubility concurrently with carrying out apolymerization reaction.

This production method of polyimide can achieve a given purpose when avinyl ether compound is contained in a reaction solution in addition tothe above-mentioned acid dianhydride and diamine to be polymerized.Depending on a specific purpose, all of the reaction solvent may be avinyl ether compound. Or, in terms of the solubility of a solute, thereaction solvent may be a mixture of a vinyl ether compound and asolvent other than the vinyl ether compound.

In terms of safety and storage stability, the solution containing avinyl ether compound preferably contains one or more kinds of solventsselected from lactones and esters.

The content of a vinyl ether compound is preferably 1 to 100% by weight,more preferably 5 to 100% by weight, still more preferably 10 to 100% byweight, with respect to the whole reaction solvent (the total weight ofliquid components in the reaction solution except substances which aresolid at 25° C., such as diamines and acid dianhydrides). It isparticularly preferred that in the case of containing a solvent inaddition to a vinyl ether compound, the vinyl ether compound becontained in an amount of 55 parts by weight or more with respect to 100parts by weight of the solvent, in terms of the reactivity of thepolyimide precursor.

This production method of polyimide precursor is preferably carried outin such a manner that the acid dianhydride is dispersed or dissolved inthe solution containing a vinyl ether compound, and then the diamine ora solution in which the diamine is dissolved is added thereto forpolymerization. In this case, the amount of time that amino groups arepresent in the reaction solution can be reduced, so that an almost idealreaction proceeds.

Since the amidation reaction between an acid anhydride and an aminogroup has a relatively high reaction rate, the amidation reaction isaccelerated by the addition of a diamine. It is preferred that thecontent of a diamine in the reaction solution be smaller than that of anacid dianhydride because, in this case, terminals of an amic acid thusproduced by the reaction are acid anhydride groups, so that hemiacetalester bonds are prevented from decomposition.

In general, acid dianhydrides have low solubility. A possible reactionof an acid dianhydride with a diamine in a non-amide solvent is areaction of a slightly dissolved acid dianhydride with a diamine in asolvent, or a solid-liquid reaction of a dispersed solid-state aciddianhydride with a diamine solution.

The addition of a diamine by the above procedure leads to the formationof an amic acid, and in most cases, the amic acid is precipitated fromthe reaction solution. It is presumed that the precipitated amic acid isthen gradually hemiacetal-esterified by the vinyl ether compound in thereaction solution and thereby dissolved in the reaction solution, sothat polymerization proceeds gradually.

In the case of adding an diamine or diamine solution later, there is noparticular limitation imposed on the adding method. If, however, adiamine or diamine solution in required quantity is added all at once,the temperature of the reaction solution may be increased by reactionheat. Accordingly, it is preferred to add an diamine or diamine solutiongradually over time or in several batches.

Since hemiacetal-esterification reaction is very sensitive to moisture,it is preferred to carry out the reaction by a method which is capableof preventing ingress of moisture as much as possible. Consequently,rather than adding a solid-state diamine through the opening of areaction container, it is preferred to dissolve a solid-state diamine ina preliminarily-dehydrated solvent and add the resultant solution in adropwise manner, so that it is possible to prevent ingress of moistureand easy to control the added amount of the diamine. Furthermore, interms of preventing side reactions, it is preferred that a moisturecontent of the solution containing a vinyl ether compound be 1% byweight or less. Additionally, in terms of preventing side reactions, itis preferred for the solution containing a vinyl ether compound tocontain substantially no water and active hydrogen other than derivedfrom said acid dianhydride and diamine. It is to be noted that thewording “to contain substantially no” means that the amount of watercontained in the solution containing a vinyl ether compound is too smallto observe a decrease in reaction yield, which is due to water and anactive hydrogen other than derived from said acid dianhydride anddiamine.

In the case of adding a diamine solution later, diamine concentration inthe solution is appropriately selected, and it is preferably from 0.1 to50% by weight, more preferably from 1 to 40% by weight.

If diamine concentration is less than 0.1% by weight, the concentrationof the reaction solution is diluted, resulting in the possibility thatthe reaction rate is decreased or no high-molecular-weight polyimideprecursor is obtained. If the concentration is more than 50% by weight,a problem arises that subtle control of the added amount of the diamineis difficult.

In the polyimide precursor production method of the present invention,it is also possible to disperse or dissolve a diamine in a solutioncontaining a vinyl ether compound, followed by the addition of an aciddianhydride or other components for polymerization.

As described above, to proceed with an ideal reaction, the method ofadding an diamine later is preferred. However, in the case of a reactionsystem containing an excess of vinyl ether compound, a desired polyimideprecursor can be obtained also by the method of adding an aciddianhydride to a diamine solution.

In the above polyimide precursor production method, it is preferred tocarry out a reaction in the solution containing a vinyl ether compoundat 0 to 45° C. At a reaction temperature of less than 0° C., thereaction rate is significantly decreased, resulting in deterioratedproductivity. At a reaction temperature of more than 45° C., sidereactions such as thermal decomposition of hemiacetal ester bonds arelikely to occur, resulting in a decrease in yield.

The polyimide precursor of the present invention preferably comprisesrepeating units represented by the formula (1) of 100 mole %, in termsof the storage stability during the period prior to forming a film. Ifrepeating units represented by the formula (1) contain those having astructure provided with a carboxylic acid by cutting the hemiacetalester bond, decomposition of the hemiacetal ester bonds can proceedeasily due to a catalytic effect of the resulting carboxylic acid.

However, even in the case where repeating units represented by theformula (1) contains those having a structure a carboxylic group bycutting the hemiacetal ester bond in some amount, pattern formation ispossible. Therefore, the polyimide precursor contained in thephotosensitive resin composition of the present invention preferablycomprises repeating units represented by the formula (1) of 70 mole % ormore, more preferably 90 mole % or more, and still more preferably 98mole % or more.

Furthermore, if no active hydrogen is contained, repeating units of apolymer such as a polyimide precursor and/or a polybenzoxazole precursorand repeating units represented by the formula (1) may present togetherin the polyimide precursor of the present invention. To form a patternwith excellent shape, however, repeating units represented by theformula (1) preferably account for at least 25 mole % of all therepeating units contained in the polyimide precursor of the presentinvention, more preferably 50 mole % or more, still more preferably 70mole % or more, and particularly preferably 90 mole % or more.

Examples of polyimide precursors, polybenzoxazole precursors and otherpolymer compounds, all of which containing no active hydrogen, includerepeating units of polyamic esters, repeating units of polyamide phenolesters, repeating units of polyamide phenol ethers, polyphenyleneethers, polyphenylenes and polyesters.

In the polyimide precursor of the present invention, in terms of storagestability, it is preferred that terminals of a polymer are each blockedwith an acid anhydride group or a structure containing no activehydrogen. For instance, in the case of an amine-terminal polyimideprecursor, examples of the method of blocking terminals with an acidhydride group or a structure containing no active hydrogen include anamidation method using acetic anhydride, a method of changing terminalsinto an amic acid by using an acid anhydride such as phthalic anhydrideor 2,3-naphthalic anhydride, etc. When the terminals are aromaticcarboxylic acids, even if the terminals have an active hydrogen, theyreact with a vinyl ether at room temperature for hemiacetalesterification, so that there is no decrease in storage stability inthis case.

To have increased sensitivity when made into a photosensitive resincomposition and to provide a pattern shape capable of exactlyreproducing a mask pattern, the polyimide precursor of the presentinvention preferably has a transmittance of at least 5% or more, morepreferably 15% or more at any of exposure wavelengths when made into a 1μm-thick film. Polyimide precursors having high transmittance at theexposure wavelengths can produce less loss of irradiated light,resulting in a photosensitive resin composition having high sensitivity.

When made into a 1 μm-thick film and exposed with a high-pressuremercury lamp, which is a general exposing source, the polyimideprecursor of the present invention preferably has a transmittance of 5%or more, more preferably 15%, and still more preferably 50% or more forone electromagnetic wave selected from the group consisting ofelectromagnetic waves having wavelengths of at least 436 nm, 405 nm and365 nm.

The weight-average or number-average molecular weight of the polyimideprecursor is preferably from 3,000 to 1,000,000, more preferably from5,000 to 500,000, and still more preferably from 7,000 to 100,000,depending on the intended application. If the weight-average ornumber-average molecular weight of the polyimide precursor is less than3,000, it is difficult to impart sufficient strength to a coating orfilm made of the polyimide precursor. Furthermore, after the polyimideprecursor is made into a polyimide by heating treatment, etc., lowstrength is imparted to a film of the polyimide. On the other hand, ifthe weight-average or number-average molecular weight exceeds 1,000,000,increased viscosity and thereby decreased solubility is imparted to thepolyimide precursor, so that it is difficult to obtain a coating or filmhaving a smooth surface and constant thickness.

It is to be noted that the weight-average molecular weight used hereinis a molecular weight that can be obtained by known methods, and anexample of which is a polystyrene equivalent molecular weight obtainedby the gel permeation chromatography (GPC). Furthermore, thenumber-average molecular weight used herein can be obtained by, forexample, a method of obtaining a number-average molecular weight fromthe integral ratio of two peaks observed in ¹H-NMR spectra, the firstpeak being derived from terminal repeating units and the second fromnon-terminal repeating units.

II. Resin Composition

The resin composition according to the present invention contains thepolyimide precursor according to the present invention. In the resincomposition of the present invention, two or more kinds of polyimideprecursors synthesized separately may be blended and used. In accordancewith the purpose, a polyimide precursor synthesized using a primaryvinyl ether compound, a polyimide precursor synthesized using asecondary vinyl ether compound and a polyimide precursor synthesizedusing a tertiary vinyl ether compound may be appropriately mixed andused.

<Polyimide Precursor Resin Composition>

The polyimide precursor resin composition of the present inventioncomprises the polyimide precursor of the present invention and a vinylether compound.

The polyimide precursor resin composition of the present inventioncontains the vinyl ether compound, thereby, storage stabilitydrastically improves.

When the polyimide precursor is isolated, the polyimide precursor can behydrolyzed by the action of moisture in the air or the like in a storageprocess with time, and can gradually change back into a polyamic acid.Particularly, unlike relatively stable aliphatic hemiacetal ester bondsmade of aliphatic carboxylic acids and vinyl ether compounds, while areaction of aromatic hemiacetal ester bonds obtained by a reaction of anaromatic carboxylic acid and a vinyl ether compounds progresses at roomtemperature by merely mixing the aromatic carboxylic acid and the vinylether compound, the aromatic hemiacetal ester bonds are often hydrolyzedby reaction with moisture in the air if the aromatic hemiacetal esterbonds exist alone.

However, if polyimide precursors having a hemiacetal ester bond coexistwith vinyl ether compounds, carboxylic acids produced by hydrolysis arehemiacetal esterified again. That is, similarly as polyimide precursorshaving a hemiacetal ester bond right after synthesis, polyimideprecursors in which all carboxyl groups are substantially hemiacetalesterified can be obtained. Therefore, the polyimide precursor of thepresent invention coexists with the vinyl ether compound, and thereby,has excellent storage stability when the polyimide precursor is used forthe resin composition.

Further, if the polyimide precursor coexists with the vinyl ethercompound, acetaldehyde produced together with a polyamic acid is hardlyoxidized, and hardly becomes acetic acid. In addition, since an alcoholalso becomes an acetal compound by an exchange reaction with otherhemiacetal ester bonds, as a result, no active hydrogen is contained inthe resin composition.

Therefore, if an excess amount of vinyl ether compound is contained inthe resin composition with respect to the amount of compounds containingactive hydrogens, a polyamic acid formed by reaction with activehydrogens promptly forms the hemiacetal ester bond so that properties ofthe resin composition are substantially unchanged. Due to such acontinuous cycle, moisture which immixes into the resin composition fromthe air or the like is consumed and the hemiacetal ester bond isreproduced. Thus, the resin composition exhibits excellent solutionstability.

The content of the vinyl ether compound is preferably from 1 weight % to90 weight %, more preferably from 5 weight % to 70 weight %, of thetotal amount of the polyimide precursor resin composition including asolvent. In addition, if the polyimide precursor resin compositioncontains a solvent, 55 parts by weight or more of the vinyl ethercompound is preferably contained with respect to 100 parts by weight ofthe solvent from the viewpoint of storage stability of the polyimideprecursor. The vinyl ether compound contained in the resin compositionof the present invention may serve as the solvent depending on selectionof the structure thereof. In that case, a solvent for dissolving,dispersing or diluting the polyimide precursor resin composition may notbe contained in the polyimide precursor resin composition.

The more amount of the vinyl ether compound increases, the moreexcellent storage stability is obtained. On the other hand, in the caseof using a polyimide precursor containing particularly many aromaticskeletons, solubility tends to decrease.

Therefore, from the viewpoint of attaining excellent storage stability,the amount of the vinyl ether compound is preferably as much as possibleto the extent that a dissolved solid is not precipitated out of thepolyimide precursor resin composition.

In addition, it is preferred that the vinyl ether compound used in thesynthesis of the polyimide precursor of the present invention is used.However, a vinyl ether compound which is different from the vinyl ethercompound used in the synthesis of the polyimide precursor may also beused. Also, a plurality of vinyl ether compounds may coexist. In thecase of a photosensitive resin composition containing a polyimideprecursor having various types of protecting moieties, a plurality ofvinyl ether compounds used in preparation of various types of protectingmoieties preferably coexist, from the viewpoint of stabilizing theintroduction rate of the protecting moieties. Primary, secondary andtertiary vinyl ether compounds may be appropriately mixed and used.

Since the vinyl ether compound may serve as the solvent depending on theselection thereof, the content of the vinyl ether compound isappropriately selected according to the kind of vinyl ether compound.

In the polyimide precursor resin composition of the present invention,the solid content of the polyimide precursor is preferably from 0.1weight % to 80 weight %, more preferably from 0.5 weight % to 50 weight%, of the total amount of the resin composition including a solvent,from the viewpoint of film properties of a film to be obtained,particularly, film strength and heat resistance. If the solid content isless than 0.1 weight %, the film thickness of a coating film to beobtained may be thin and following capability to a substrate havingconvexoconcaves on surfaces may decrease, thereby resulting in unevencoating. On the other hand, if the solid content exceeds 80 weight %,the viscosity of the resin composition increases so that uneven filmthickness is likely to occur due to volatilization of the solvent duringcoating or the like.

In the resin composition of the present invention, the solid content ofthe polyimide precursor is preferably 30 weight % or more and morepreferably 50 weight % or more, with respect to the total solid contentof the resin composition excluding the solvent and the vinyl ethercompound hereinafter described, from the viewpoint of physicalproperties of a film to be obtained, particularly, film strength andheat resistance.

<Photosensitive Resin Composition>

The inventor has studied the hemiacetal ester bond of the polyimideprecursor in detail and has found that the hemiacetal ester bond isdecomposed in the presence of acid or base or decomposed by heating inthe presence of acid or base to become a polyamic acid and a vinylether, or a polyamic acid, acetaldehyde and an alcohol. Therefore, ifthe polyimide precursor having the repeating unit represented by theformula (1) and a photoacid or photobase generator are used incombination utilizing such a reaction, the hemiacetal ester bond isbroken exclusively in an exposed portion by the effect of generated acidor base, and a difference in dissolving rate can be made in the exposedportion and unexposed portion.

For example, by developing an exposed and unexposed portion, in whichthe exposed portion exclusively results in an appearance of a polyamicacid soluble in a basic aqueous solution, with a basic aqueous solution,a positive type pattern, in which the unexposed portion remains, can beobtained. On the other hand, while the polyimide precursor easilydissolves in a solvent such as γ-butyrolactone, the polyamic acid hardlydissolves in such a solvent. Hence, by developing the exposed andunexposed portion with a solvent such as γ-butyrolactone afterdecomposing the hemiacetal ester bond, a negative type pattern, in whichthe exposed portion remains, can be also obtained.

In addition, by controlling exposure conditions and an environment uponexposure, conditions and an environment of heating after exposure and soon, imidization of the polyimide precursor can proceed at the same timeas decomposition of the hemiacetal ester bond. In this case, thepolyimide precursor in the exposed portion partially becomes thepolyimide, which has poor solubility, so that a negative type patterncan be obtained by developing the unexposed portion with a solvent.

In the present invention, both positive image and negative image can beobtained by changing process conditions and a developer being used. Inthis way, the photosensitive resin composition of the present inventioncan achieve a large dissolution contrast irrespective of the chemicalstructure of a polyimide to be finally obtained, and, as a result, apattern with excellent shape can be achieved while keeping a sufficientprocess margin.

Since the photoacid or photobase generator in the photosensitive resincomposition of the present invention catalytically acceleratesdecomposition of the hemiacetal ester bond, it is possible to obtain apattern with the use of a small amount of acid or base. Morespecifically, the photosensitive resin composition of the presentinvention having the hemiacetal ester bonds and the photoacid orphotobase generator in combination can reduce the added amount of thephotoacid or photobase generator, which is expensive per unit weight,thereby, cost can be reduced. Furthermore, the photosensitive resincomposition of the present invention is highly sensitive. Further, theamount of residue of components derived from the photobase generator ina cured film (polyimide film) to be finally obtained can be reduced.

Also, the inventor has studied the hemiacetal ester bond of thepolyimide precursor in detail and has found that, by heating atrelatively low temperature, the hemiacetal ester bond dissociates into apolyamic acid and a vinyl ether compound, or is hydrolyzed into apolyamic acid and a vinyl ether, or a polyamic acid, acetaldehyde and analcohol. Therefore, utilizing such a reaction, the polyimide precursorhaving the repeating unit represented by the formula (1) can partiallyor completely be an amic acid structure by causing the abovedissociation or hydrolysis reaction by heating the polyimide precursorhaving the repeating unit represented by the formula (1) under moderateconditions. An amic acid portion has a carboxyl group and exhibits highsolubility in a basic solution, and it is possible to change theproportion of changing a hemiacetal ester portion into the amic acidportion by appropriately controlling heating conditions. If thepolyimide precursor in which solubility in such a basic solution iscontrolled and a compound which particularly generates a carboxylic acidby the action of light among photoacid generators are used incombination, the exposed portion dissolves in the basic solution since acarboxyl group is generated to increase hydrophilicity of the exposedportion, while the unexposed portion does not dissolve in the basicsolution since the unexposed portion remains hydrophobic. Thereby, thepositive type pattern, in which the unexposed portion remains, can beobtained.

In this way, the photosensitive resin composition of the presentinvention can achieve a large dissolution contrast irrespective of thechemical structure of a polyimide to be finally obtained, and, as aresult, a pattern with excellent shape can be achieved while keeping asufficient process margin, by controlling solubility of the polyimideprecursor in the basic solution using a simple means of heating.

A first photosensitive resin composition according to the presentinvention comprises the polyimide precursor according to the presentinvention and the photoacid generator.

By using the photoacid generator, a photosensitive resin compositionhaving high sensitivity can be obtained since there are many kinds ofcommercially available photoacid generators so that the range of optionsto select photoacid generators and highly sensitive photoacid generatorscan be selected. In addition, by heating after exposure to generate anacid, it is possible for some kinds of photoacid generators to have achemical amplification mechanism, in which the generated acid decomposesundecomposed photoacid generators and further produces acid. In thiscase, a photosensitive resin composition having higher sensitivity canbe obtained.

As the photoacid generator of the present invention, any of knownphotoacid generators may be used without any particular limitation ifthe photacid generators decompose and generate an acid by absorbingelectromagnetic waves. As the photoacid generator used in the presentinvention, a compound which itself causes a reaction such asdecomposition or intramolecular rearrangement due to exposure ofelectromagnetic waves, and changes from neutral to acid is suitablyused. The photoacid generator may be used alone or in combination of twoor more kinds. In the present invention, the electromagnetic waves maybe ones which are capable of causing a decomposition reaction in amolecule of a compound, which include not only electromagnetic waves ofwavelength in visible or non-visible region but also particle beams suchas electron beams, and radiations or ionizing radiations, whichcollectively refer to the electromagnetic waves and the particle beams.

Examples of a photoacid generator which generates an acid other than acarboxylic acid are iodonium salts such as diphenyliodonium sulfonate,sulfonium salts such as triphenyl sulfonium triflate, benzyl esters suchas o-nitrobenzyl sulfonate, acetic acid o-nitrobenzyl acetate, phenylsulfonate esters such as 1,2,3-tris(sulfonyloxy)benzene, N-imidesulfonates such as N-phthalimide tosylate and succinimide sulfonate,diazodisulfones such as dicyclohexyl diazodisulfone, halomethyls such asbis trichloro methyl phenyl triazine, disulfones such asdiphenyldisulfone, oxime sulfonate, keto sulfone compounds and α-ketosulfonates.

On the other hand, among photoacid generators, as a compound whichgenerates a carboxylic acid by the action of light, it is preferred touse a compound having an o-quinone diazide group. The compound having ano-quinone diazide group has a large difference in hydrophobicity andhydrophilicity before and after exposure, thus, a large solubilitycontrast can be obtained. Also, the compound having an o-quinone diazidegroup has characteristics of being applicable to wide range of lightsource due to having high sensitivity and wide absorption band of light.Further, the compound can be easily obtained since various kinds ofstructures are commercially available. If the polyimide precursor havingthe repeating unit represented by the formula (1) and the compoundhaving an o-quinone diazide group are used in combination, ahighly-sensitive and low-cost photosensitive resin composition can beobtained.

Examples of the compound having an o-quinone diazide group includeo-benzoquinone diazide sulfonic acid ester or sulfonic acid amide,o-naphthoquinone diazide-4-sulfonic acid ester or sulfonic acid amide,and o-naphthoquinone diazide-5-sulfonic acid ester or sulfonic acidamide. The compound having an o-quinone diazide group can be obtained,for example, by a condensation reaction of any of o-quinone diazidesulfonyl chlorides and a hydroxy compound, an amino compound or the likein the presence of a dehydrochlorination agent.

Examples of the o-quinone diazide sulfonyl chlorides to be used includebenzo quinone-1,2-diazide-4-sulfonyl chloride,naphthoquinone-1,2-diazide-5-sulfonyl chloride andnaphthoquinone-1,2-diazide-4-sulfonyl chloride, but are not necessarilylimited thereto.

As a compound which reacts with the o-quinone diazide sulfonylchlorides, the hydroxy compound is preferred from the viewpoint ofphotosensitive property. Examples of the hydroxy compound to be usedinclude hydroquinone, resorcinol, pyrogallol, bisphenol A,bis(4-hydroxyphenyl)methane, 2,2-bis(4-hydroxyphenyl)hexafluoropropane,2,3,4-trihydroxy benzophenone, 2,3,4,4′-tetrahydroxy benzophenone,2,2′,4,4′-tetrahydroxy benzophenone, 2,3,4,2′,3′-pentahydroxybenzophenone, 2,3,4,3′,4′,5′-hexahydroxy benzophenone,bis(2,3,4-trihydroxyphenyl)methane, bis(2,3,4-trihydroxyphenyl)propane,4b,5,9b,10-tetrahydro-1,3,6,8-tetrahydroxy-5,10-dimethylindeno[2,1-a]indene,tris(4-hydroxyphenyl)methane and tris(4-hydroxyphenyl)ethane. Thehydroxy compound to be used is not necessarily limited thereto.

In addition, examples of the amino compound to be used includep-phenylenediamine, m-phenylenediamine, 4,4′-diamino diphenyl ether,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulfone,4,4′-diaminodiphenyl sulfide, o-aminophenol, m-aminophenol,p-aminophenol, 3,3′-diamino-4,4′-dihydroxybiphenyl,4,4′-diamino-3,3′-dihydroxybiphenyl,bis(3-amino-4-hydroxyphenyl)propane,bis(4-amino-3-hydroxyphenyl)propane,bis(3-amino-4-hydroxyphenyl)sulfone,bis(4-amino-3-hydroxyphenyl)sulfone,bis(3-amino-4-hydroxyphenyl)hexafluoropropane andbis(4-amino-3-hydroxyphenyl)hexafluoropropane. The amino compound to beused is not necessarily limited thereto.

As the polyimide precursor which is used in combination with thecompound which generates a carboxylic acid by the action of light, it ispreferred to use the polyimide precursor in which solubility in a basicsolution is controlled in such a manner that the proportion of changingthe hemiacetal ester portion into the amic acid portion is changed byappropriately controlling heating conditions. From this viewpoint, inthe polyimide precursor of the present invention, it is preferred thatR⁸ in the formula (2) contains two or more kinds of organic groups. Morespecifically, provided that A1 refers to a group consisting of organicgroups in which the carbon atom bonded at R⁸ in the formula (2) to theoxygen atom is a primary carbon atom; A2 refers to a group consisting oforganic groups in which said carbon atom is a secondary carbon atom; andA3 refers a group of organic groups in which said carbon atom is atertiary carbon atom in the polyimide precursor, R⁸ may be a mixturecomprising A1 and A2; A1 and A3; A2 and A3; or A1, A2 and A3, and themixture containing two or more kinds of organic groups by combining oneor more kinds of each group in the above combination. By making theprotecting moieties introduced from the hemiacetal ester bonds into twoor more kinds of protecting moieties having different decompositiontemperature, it becomes possible to selectively control the rate ofdecomposition of the hemiacetal ester bonds and to form more stably apattern.

The amount of the photoacid generator is preferably from 0.005 weight %to 20 weight % of the total amount of the photosensitive resincomposition including a solvent, from the viewpoint of sensitivity.Also, from 0.01 weight % to 30 weight % of the photoacid generator whichgenerates an acid other than a carboxylic acid is preferably containedin the photosensitive resin composition of the present invention withrespect to the total solid content excluding a solvent and the vinylether compound hereinafter described in the photosensitive resincomposition from the viewpoint of sensitivity, and from 0.1 weight % to10 weight % is more preferably contained from the viewpoint of reducingthe amount of decomposed products derived from the photoacid generatorafter imidization. On the other hand, from 0.01 weight % to 45 weight %of the compound which generates a carboxylic acid by the action of lightis preferably contained with respect to the total solid contentexcluding a solvent and the vinyl ether compound hereinafter describedin the photosensitive resin composition from the viewpoint ofsensitivity, and from 0.1 weight % to 35 weight % is more preferablycontained from the viewpoint of reducing the amount of decomposedproducts derived from the compound which generates a carboxylic acid bythe action of light after imidization. Particularly, from the viewpointof outgassing, smaller amount of the photoacid generator is moredesirable.

On the other hand, a second photosensitive resin composition accordingto the present invention comprises the polyimide precursor of thepresent invention and the photobase generator.

Particularly, base is preferred from the viewpoint of exhibiting highreliability, particularly high insulating reliability, for applicationswhich involve contact with metal since base does not cause corrosion ofmetal.

As the photobase generator of the present invention, any of knownphotobase generators may be used without any particular limitation ifthe photobase generators decompose and generate base by absorbingelectromagnetic waves. As the photobase generator used in the presentinvention, a compound which itself causes a reaction such asdecomposition or intramolecular rearrangement due to exposure ofelectromagnetic waves, and changes from neutral to basic, generally acompound which generates a primary, secondary, or tertiary amine, issuitably used. The photobase generator may be used alone or incombination of two or more kinds.

Examples of a nonionic photobase generator include nitrobenzylurethane-based compounds such asN-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-di-isopropylamine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-bis(3-pentyl)amine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-bis(4-heptyl)amine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-dicyclopropylamine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-dicyclobutylamine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-dicyclopentylamine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-dicyclohexylamine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpyrrolidine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethyl-4-methyl-piperazine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylmorpholine,N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylthiomorpholine,N-{[(3,4-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine,N-{[(3,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine,N-{[(3,6-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine,N-{[(4,6-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine,andN-{[(5,6-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine;acyloxy imino ester-based compounds such as acetophenone oxime benzoate,acetophenone oxime valeriate, acetophenone oxime phenylacetate,benzophenone oxime benzoate, benzophenone oxime valeriate, andbenzophenone oxime benzoate; coumaric amide and derivatives thereof.

Examples of an ionic photobase generator include quaternary ammoniumsalts with halogen ion, and quaternary ammonium salts with other anionsuch as thiocyanate ion and tetraphenyl borate ion.

The amount of the photobase generator is preferably from 0.005 weight %to 20 weight % of the total amount of the photosensitive resincomposition including a solvent, from the viewpoint of sensitivity.Also, from 0.01 weight % to 30 weight % of the photobase generator ispreferably contained in the photosensitive resin composition of thepresent invention with respect to the total solid content excluding asolvent and the vinyl ether compound hereinafter described in thephotosensitive resin composition from the viewpoint of sensitivity, andfrom 0.1 weight % to 10 weight % is more preferably contained from theviewpoint of reducing the amount of decomposed products derived from thephotobase generator after imidization. Particularly, from the viewpointof outgassing, smaller amount of the photobase generator is moredesirable.

The photoacid or photobase generator used in the present inventionpreferably has absorption in at least one electromagnetic wave havingthe wavelength selected from 436 nm, 405 nm and 365 nm. The polyimideprecursor contained in the photosensitive resin composition generallyhas a strong absorption in the wavelength of 330 nm or less. Therefore,it is preferred that the photoacid or photobase generator contained inthe photosensitive resin composition generates acid or base by theaction of light in the wavelength region that the polyimide precursoreasily transmits, and has absorption in the wavelength region of 330 nmor more. Further, it is preferred that the photoacid or photobasegenerator has absorption in at least one light having the wavelengthselected from 436 nm, 405 nm and 365 nm, which have high strength amongemission wavelengths of high pressure mercury lamp being a light sourcegenerally used in exposure. It is particularly preferred that thephotoacid or photobase generator has absorption in the wavelengthselected from 436 nm and 405 nm.

In addition, specifically, the photoacid or photobase generator used inthe present invention preferably has a molar absorbance coefficient of 1or more, more preferably 10 or more, and still more preferably 50 ormore, in any of wavelengths of at least 365 nm or more.

Further, from the viewpoint of reducing the amount of decomposedproducts derived from the photoacid or photobase generator remaining ina film after imidization, the rate of weight loss by heating at 400° C.of the polyimide obtained from the resin composition is preferably 50%or less, more preferably 30% or less, and still more preferably 10% orless, under nitrogen atmosphere.

Particularly, in the case of reducing the amount of decompositionresidue remaining in the polyimide, the rate of weight loss by heatingat 300° C. of the polyimide obtained from the resin composition ispreferably 50% or less, more preferably 30% or less, and still morepreferably 10% or less, under nitrogen atmosphere.

The first and second photosensitive resin compositions according to thepresent invention preferably contain the aforementioned vinyl ethercompound from the viewpoint of drastically improving storage stability.

In the first and second photosensitive resin compositions of the presentinvention, the solid content of the polyimide precursor is preferablyfrom 0.1 weight % to 80 weight %, more preferably from 0.5 weight % to50 weight %, of the total amount of the photosensitive resin compositionincluding a solvent, from the viewpoint of film properties of a patternto be obtained, particularly, film strength and heat resistance. If thesolid content is less than 0.1 weight %, the film thickness of a coatingfilm to be obtained may be thin and following capability to a substratehaving convexoconcaves on surfaces may decrease, thereby resulting inuneven coating. On the other hand, if the solid content exceeds 80weight %, the viscosity of the resin composition increases so thatuneven film thickness is likely to occur due to volatilization of thesolvent during coating or the like.

In the photosensitive resin composition of the present invention, thesolid content of the polyimide precursor is preferably 30 weight % ormore and more preferably 50 weight % or more, with respect to the totalsolid content of the photosensitive resin composition excluding asolvent and the vinyl ether compound hereinafter described in thephotosensitive resin composition, from the viewpoint of film propertiesof a pattern to be obtained, particularly, film strength and heatresistance.

<Common Characteristics of Resin Composition>

The resin composition containing the polyimide precursor according tothe present invention (polyimide precursor resin composition andphotosensitive resin composition) preferably has the following commoncharacteristics.

It is preferred that the resin composition of the present inventioncontains no active hydrogen and no compound having an active hydrogen.Particularly, it is preferred that the resin composition contains nowater. If these components are contained in the resin composition, thehemiacetal ester bond gradually decomposes and storage stabilitydecreases.

If the hemiacetal ester bond coexists with a compound having an activehydrogen such as a hydroxyl group, an exchange reaction between thehemiacetal ester bond and the active hydrogen may be caused. Since thehemiacetal bond is generally more stable than the hemiacetal ester bond,if the polyimide precursor and a compound containing a hydroxyl groupcoexist, the hemiacetal ester bond is consumed by the hydroxyl group,and a polyamic acid is produced. That is, if the polyimide precursorcoexists with the compound having an active hydrogen such as a hydroxylgroup, stability of the polyimide precursor decreases. The rate ofdecomposition reaction of the hemiacetal ester bond varies depending onthe chemical structure thereof, and there is a tendency that the fasterthe rate of reaction producing the hemiacetal ester bond is, the fasterthe rate of decomposition is.

In addition, from the viewpoint of attaining excellent storagestability, the content of water in the resin composition is preferably 1weight % or less, more preferably 0.1 weight % or less. Further, theresin composition substantially containing no water is most preferable.Herein, “substantially containing no water” means that the content ofwater in the composition is low to the extent that decrease of storagestability due to water cannot be observed. Specifically, it means thestate in which percentage of the water content in the composition isabout less than 0.005 weight %, further less than 0.001 weight %.

Further, the hydrolysis of the hemiacetal ester bond catalyticallyproceeds in the presence of acid or base. Therefore, since no acid orbasic material is substantially contained in the resin composition,storage stability of the polyimide precursor of the present inventioncontaining 100% of hemiacetal ester bonds can be improved. If acid orbasic materials are contained in the resin composition, the polyimideprecursor decomposes to give a polyamic acid, and further, molecularweight tends to decrease.

Herein, “substantially containing no acid or basic material” means thatthe content of acid or basic materials in the composition is low to theextent that decrease of storage stability due to acid or basic materialscannot be observed. Specifically, it means the state in which thecontent percentage of acid or basic materials in the composition isabout less than 0.005 weight %, further less than 0.001 weight %.

As a solvent for dissolving, dispersing or diluting the resincomposition, any of various types of general-purpose solvents can beused. Alternatively, the reaction solvent when the polyimide precursoris prepared can be used without any change. The solvent may be usedalone or in combination of two or more kinds. However, to improvestorage stability of the resin composition, it is preferred to use asolvent containing no active hydrogen. Further, a solvent containing nonitrogen atom such as an amide bond in a skeleton is preferred for thesame purpose. In addition, it is preferred that a solvent containing anitrogen atom is not contained.

Also, a solution obtained from the synthesis reaction of the polyimideprecursor may be used without any change, or other components may bemixed thereto, if required.

Examples of available general-purpose solvents are ethers such asdiethyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether,ethylene glycol diethyl ether, propylene glycol dimethyl ether, andpropylene glycol diethyl ether; ketones such as methyl ethyl ketone,acetone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone;esters such as ethyl acetate, butyl acetate, n-propyl acetate, i-propylacetate, n-butyl acetate, i-butyl acetate, acetic acid ester of theglycol monoethers (for example, methyl cellosolve acetate, and ethylcellosolve acetate), methoxy propyl acetate, ethoxy propyl acetate,dimethyl oxalate, methyl lactate, and ethyl lactate; halogenatedhydrocarbons such as methylene chloride, 1,1-dichloroethane,1,2-dichloroethylene, 1-chloropropane, 1-chlorobutane, 1-chloropentane,chlorobenzene, bromobenzene, o-dichlorobenzene, and m-dichlorobenzene;lactones such as γ-butyrolactone; sulfoxides such as dimethyl sulfoxide;and other organic polar solvents. Further, examples are aromatichydrocarbons such as benzene, toluene and xylene, and other organicnonpolar solvents. These solvents are used alone or in combination.

Among the above, it is preferred to use lactones or sulfoxides, from theviewpoint of being able to prepare a highly-concentrated solution havinghigh storage stability and excellent solubility.

The resin composition of the present invention may be a simple mixturemerely made of the polyimide precursor, the above-mentioned essentialcomponents and a solvent, if required. The resin composition may beprepared by appropriately compounding other components such assurfactants.

Various organic or inorganic low molecular or polymer compounds may becompounded besides the above, in order to impart process property orvarious functionalities to the resin composition of the presentinvention unless the object and effect of the present invention areimpaired. For example, dyes, surfactants, leveling agents, plasticizers,microparticles and so on may be used. The microparticles may includeorganic microparticles such as polystyrene and polytetrafluoroethylene,and inorganic particles such as colloidal silica, carbon andphyllosilicate, which may be porous or have a hollow structure. Examplesof the function or form of these microparticles include pigments,fillers and fibers.

In the photosensitive resin composition of the present invention,addition of a sensitizer may be effective in order to improvesensitivity by the photoacid or photobase generator being sufficientlyable to utilize the energy of electromagnetic waves of the wavelengththat the polyimide precursor transmits.

Particularly, in the case that the polyimide precursor also hasabsorption in the wavelength of 360 nm or more, the effect of additionof the sensitizer is large. Specific examples of compounds calledsensitizers include thioxanthone, diethyl thioxanthone and derivativesthereof, coumarins and derivatives thereof, ketocoumarin and derivativesthereof, ketobiscoumarin and derivatives thereof, cyclopentanone andderivatives thereof, cyclohexanone and derivatives thereof, thiopyryliumsalt and derivatives thereof, and thioxanthenes xanthenes, andderivatives thereof. However, it is preferred that an active hydrogengroup is not contained in these compounds from the viewpoint of storagestability of the photosensitive resin composition.

Specific examples of coumarin, ketocoumarin and derivatives thereofinclude 3,3′-carbonyl biscoumarin, 3,3′-carbonylbis(5,7-dimethoxycoumarin), and 3,3′-carbonyl bis(7-acetoxy coumarin).

Specific examples of thioxanthone and derivatives thereof includediethyl thioxanthone, and isopropylthioxanthone.

Further, other examples include benzophenone, acetophenone,phenanthrene, 2-nitrofluorene, 5-nitroacenaphthene, benzoquinone,2-ethyl anthraquinone, 2-tert-butylanthraquinone, 1,2-benzanthraquinone,and 1,2-naphthoquinone.

Since the sensitizer exhibits particularly excellent effect by using incombination with the photoacid or photobase generator, a sensitizerwhich exhibits optimum sensitization action is appropriately selecteddepending on a structure of the photoacid or photobase generator.

The compounding ratio of other optional components is appropriatelyselected depending on properties of the optional components and is notparticularly limited. The compounding ratio is preferably from 0.1weight % to 30 weight % with respect to the total solid contentexcluding the solvent and the vinyl ether compound in the resincomposition. If the ratio is less than 0.1 weight %, it is difficult toexhibit the effect of added additives. If the ratio exceeds 30 weight %,it is difficult to reflect the characteristics of the resin curedproduct finally obtained on an end product.

The resin composition of the present invention can be used for variouscoating processes or molding processes to produce a film or athree-dimensional molded body.

The polyimide obtained from the resin composition of the presentinvention contains a small amount of decomposition residues derived fromprotecting components since eliminatability of hemiacetal esterifiedsite of the precursor is excellent. Therefore, the polyimide also keepsoriginal properties such as heat resistance, dimensional stability andinsulation, which are excellent.

For example, the 5% loss in weight temperature of the polyimide obtainedfrom the resin composition of the present invention measured undernitrogen atmosphere is preferably 250° C. or more, more preferably 300°C. or more. Particularly, in the case that the polyimide obtained fromthe resin composition of the present invention is used for applicationssuch as electronic components, the production method of which includes asolder reflow process, if the 5% loss in weight temperature is 300° C.or less, there is a risk that defects such as bubbles may occur due tocracked gas generated in the solder reflow process.

Herein, the 5% loss in weight temperature means a temperature at whichweight of a sample is reduced by 5% of an initial weight (that is tosay, a temperature at which the weight of the sample is reduced to 95%of the initial weight) when a weight decrement is measured by means ofthe thermogravimetric analyzer. Similarly, a 10% loss in weighttemperature means a temperature at which weight of a sample is reducedby 10% of an initial weight.

The glass transition temperature of the polyimide obtained from theresin composition of the present invention is preferably 260° C. or morefrom the viewpoint of heat resistance. The glass transition temperatureis important for electronic members which include a solder reflowprocess. In applications which may include a thermoforming process suchas an optical waveguide, the glass transition temperature is preferablyabout 120° C. to 400° C., more preferably about 200° C. to 370° C.

Herein, if the polyimide obtained from the resin composition can beformed into a film, the glass transition temperature in the presentinvention can be obtained from a peak temperature of tan δ (tan δ=losselastic modulus (E″)/storage elastic modulus (E′)) by a dynamicviscoelasticity measurement. The dynamic viscoelasticity measurement canbe conducted by, for example, a viscoelasticity analyzer (product name:Solid Analyzer RSA II, manufactured by Rheometric Scientific Inc.) at afrequency of 1 Hz and a heating rate of 5° C./min. If the polyimideobtained from the resin composition cannot be formed into a film, theglass transition temperature in the present invention can be obtainedfrom a temperature of a flexion point on baseline of a differentialscanning calorimetry (DSC).

From the viewpoint of dimensional stability, the linear thermalexpansion coefficient of the polyimide obtained from the resincomposition of the present invention is preferably 60 ppm or less, morepreferably from 0 ppm to 40 ppm. In the case of forming a film on asilicon wafer in a production process of semiconductor elements, thelinear thermal expansion coefficient is preferably from 0 ppm to 25 ppmfrom the viewpoint of adhesion property and warp of a substrate. Herein,the linear thermal expansion coefficient in the present invention can bedetermined by analyzing a film of the polyimide obtained from the resincomposition of the present invention by means of a thermomechanicalanalyzer (TMA). The linear thermal expansion coefficient is a valuemeasured by means of the thermomechanical analyzer (for example, productname: Thermo Plus TMA8310, manufactured by Rigaku Corporation) under thecondition including a heating rate of 10° C./min and a tensile load of 1g/25,000 μm² so that each load per area of cross section of anevaluating sample is equal.

Similarly, from the viewpoint of dimensional stability, the humidityexpansion coefficient of the polyimide obtained from the resincomposition of the present invention is preferably 40 ppm or less, morepreferably 20 ppm or less. Ideally, 10 ppm to 0 ppm is preferred.

Herein, the humidity expansion coefficient in the present invention canbe determined by analyzing a film of the polyimide obtained from theresin composition of the present invention by means of a humidityvariable mechanical analyzer (S-TMA). A difference between samplelengths of a sample being stable in an environment with a temperature of25° C. and a relative humidity of 20% and the sample the relativehumidity being changed to 50% and being stable using the humidityvariable mechanical analyzer (for example, product name: modified ThermoPlus TMA8310, manufactured by Rigaku Corporation), is divided bydifference in humidity (in this case 50 minus 20 is 30). Then, the valueobtained thereby is divided by the sample length at 20% RH. Thereby, thehumidity expansion coefficient can be obtained. A tensile load is 1g/25,000 μm² so that each load per area of cross section of anevaluating sample is equal.

III. Pattern Forming Method

The pattern forming method of the present invention comprises anexposure step of irradiating a surface of a film or molded body of thephotosensitive resin composition according to the present invention withelectromagnetic waves in a predetermined pattern, and a developing stepof developing either an exposed or unexposed portion with a solventwhich is capable of dissolving the exposed or unexposed portion as adeveloper.

In the photosensitive resin composition containing the polyimideprecursor and the photoacid or photobase generator, the hemiacetal esterbond of the polyimide precursor is decomposed by the action of acid orbase generated from the photoacid generator or photobase generator dueto the action of light. Thereby, the solubility of the photosensitiveresin composition in an aqueous solution or an organic solvent changes.By utilizing this change in solubility, when exposure is performed in adesired pattern and a soluble portion is dissolved with a good solvent,a pattern can be obtained.

Particularly, in the case of the photosensitive resin compositioncontaining the polyimide precursor and the compound which generates acarboxylic acid by the action of light, the pattern forming method ofthe present invention includes a heating step of heating a film ormolded body made of the photosensitive resin composition containing thepolyimide precursor and the compound which generates a carboxylic acidby the action of light upon or after forming the film or molded body; anexposure step of irradiating the surface of the film or molded bodyafter the heating step with electromagnetic waves in a predeterminedpattern; and a developing step of developing the film or molded bodywith a basic solution as a developer.

The film or molded body made of the photosensitive resin composition ofthe present invention can be produced by any of known methods. Forexample, the film can be obtained by coating the photosensitive resincomposition of the present invention on a substrate and drying thecomposition. Herein, the substrate is an object on which a polyimidefilm is to be formed. Examples of the substrate are inorganic materialsincluding metals such as copper and stainless, silicon, metal oxides,metallic nitrides, and organic materials such as polyimides andpolybenzoxazole. Though adhesion and soon slightly vary from substrateto substrate, pattern forming and properties of film to be obtained arenot substantially different. Hence, in the present invention, thesubstrate is not particularly limited.

Examples of the coating method include a spin coating method, a diecoating method and a dip coating method, but are not particularlylimited thereto. Any of known methods can be used. The pattern formingmethod of the present invention can also be used for a film obtained byany of the coating methods.

Drying can be performed accordingly by any of known heating methods suchas using a hot plate or oven.

In the exposure step, the thus obtained film or molded body isirradiated with electromagnetic waves through a photomask with a desiredpattern or directly in a pattern shape.

A light source of the exposure is not particularly limited and any knownlight source may be used. Especially in the case of an aromaticpolyimide having high heat resistance and low linear thermal expansioncoefficient, because the polyimide precursor has a strong absorption inthe wavelength of 350 nm or less, it is preferred to expose thepolyimide precursor to light at the wavelength of 360 nm or more whenused as a highly photosensitive resin composition. From the viewpoint ofthe above conditions, availability, cost for maintenance and so on, alight source such as a high-pressure mercury-vapor lamp or the like ispreferably used.

The exposure method and exposure equipment used in the exposure step isnot particularly limited. Contact exposure or indirect exposure may beperformed. Any of known means such as a stepper, a scanner, an aligner,a contact printer, a laser and electron beam lithography may be used.

Heating is performed after the exposure step and before the developingstep, if necessary.

By heating appropriately, in the exposed portion of the film or moldedbody, the decomposition of the hemiacetal ester bond by base generatedby the exposure is accelerated and changes into a carboxyl group or thelike.

The heating temperature is preferably from room temperature (23° C.) to180° C. The temperature depends on the structure of R¹ in the formula(1) and R⁸ in the formula (2) of the polyimide precursor. Generally, ifthe electron attractivity of R¹ is strong or the electron donatabilityof R⁸ is strong, the hemiacetal ester bond often decomposes at lowertemperature. In the reverse case, heating at higher temperature is oftenrequired. If the heating temperature is too high, the hemiacetal bond ofthe unexposed portion also decomposes. Hence, a temperature at which adegree of decomposition of the hemiacetal bond in the exposed portionand a degree of decomposition of the hemiacetal bond in the unexposedportion are largely different is appropriately selected.

The heating temperature is appropriately selected depending on thestructure of the polyimide precursor. The heating time may be 5 secondsto 120 minutes, preferably 30 seconds to 30 minutes, from the viewpointof productivity. A heating method may be any of known methods.

After the hemiacetal ester bond in the exposed portion is decomposed,the developing step is performed.

The photosensitive resin composition of the present invention can changethe solubility of the exposed portion and unexposed portion in varioussolvent by the action of acid or base breaking the hemiacetal esterbond.

The unexposed portion of the photosensitive resin composition of thepresent invention is hardly soluble in basic aqueous solutions, andsoluble in organic (polar) solvents including amide-based solvents. Onthe other hand, in the exposed portion, the hemiacetal ester bond of thepolyimide precursor breaks by hydrolysis due to the action of thegenerated acid or base to give a polyamic acid. Also, under thecondition that the amount of moisture is extremely low in the presenceof base with heating if necessary, the polyimide precursor is imidized,and accordingly, the hemiacetal ester bond is decomposed into an alcoholand acetaldehyde. Thus, if the amount of moisture in the film is largeor the humidity of environment is high, the hemiacetal ester bonddecomposes to give an amic acid. However, in the case that the solventis dehydrated and the environment is controlled to have no moisturesubstantially, the polyimide precursor is imidized.

The polyamic acid is soluble mainly in amide-based organic solvents,dimethyl sulfoxide and basic aqueous solutions, and is insoluble innon-amide-based organic solvents except some solvents such as dimethylsulfoxide. To the contrary, generally, polyimides, particularly aromaticpolyimides, are hardly soluble in any solvents. Hence, the solubility ofthe exposed or unexposed portion can be controlled by the conditions ofprocesses such as exposure and heating after exposure, if necessary.

When the hemiacetal ester bond decomposes to give the polyamic acid, apositive type pattern can be obtained by development with a basicaqueous solution, and a negative type pattern can be obtained bydevelopment with a non-amide-based organic solvent such asγ-butyrolactone. When the hemiacetal ester bond is imidized, a negativetype pattern can be obtained by development with a non-amide-basedorganic solvent such as γ-butyrolactone.

In this way, the photosensitive resin composition of the presentinvention can be used as a positive type or a negative type depending ondevelopers and processes.

The positive type has an advantage that more inexpensive basic aqueoussolution can be used. The negative type has an advantage that hemiacetalesterified portions in a pattern portion decomposes and decomposedproducts volatile, thus, protective group-derived residual components donot remain in a polyimide film.

Besides the above, it is possible to use a method including introducingan epoxy group, an oxetanyl group or the like, which causes across-linking reaction by base, into the polyimide precursor, subjectingthe exposed portion to insolubilization, and thus obtaining a negativetype pattern. In the case of using such a negative type photosensitivepolyimide, in which a pattern is obtained by the mechanism that thesolubility is reduced by intermolecular cross-linking, generally,crosslinked portions are less likely to thermally decompose andvolatilize. Thus, decomposition residues of photosensitivity-impartingcomponents are likely to remain in the film after imidization. Further,since development is often performed by organic solvents, applicationsto be used are limited.

The developer used in the developing step is not particularly limited. Abasic aqueous solution, an organic solvent, an acid aqueous solution, aneutral aqueous solution, and so on can be selected according to thepolyimide precursor to be used.

The basic aqueous solution is not particularly limited. Examples of thebasic aqueous solutions are a tetramethylammonium hydroxide (TMAH)aqueous solution, a potassium hydroxide aqueous solution, a sodiumhydroxide aqueous solution, a magnesium hydroxide aqueous solution, acalcium hydroxide aqueous solution, a sodium hydrogencarbonate aqueoussolution, an aqueous solution of primary, secondary or tertiary amine,and an aqueous solution of salt of hydroxide ion and ammonium ion,having a concentration of 0.01 wt % to 30 wt %, preferably 0.05 wt % to10 wt %.

A solute may be one kind only, or two or more kinds. An organic solventor the like may be contained if water is included by 50% or more,preferably 70% or more, of the total weight.

The organic solvent is not particularly limited. Examples of the organicsolvents include ethers such as diethyl ether, tetrahydrofuran, dioxane,ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propyleneglycol dimethyl ether, and propylene glycol diethyl ether; glycolmonoethers (so-called cellosolves) such as ethylene glycol monomethylether, ethylene glycol monoethyl ether, propylene glycol monomethylether, propylene glycol monoethyl ether, diethylene glycol monomethylether, and diethylene glycol monoethyl ether; ketones such as methylethyl ketone, acetone, methyl isobutyl ketone, cyclopentanone, andcyclohexanone; esters including ethyl acetate, butyl acetate, n-propylacetate, i-propyl acetate, n-butyl acetate, i-butyl acetate, acetic acidesters of the glycol monoethers such as methylcellosolve acetate andethylcellosolve acetate, methoxypropyl acetate, ethoxypropyl acetate,dimethyl oxalate, methyl lactate, and ethyl lactate; alcohols such asmethanol, ethanol, isopropanol, propanol, butanol, hexanol,cyclohexanol, ethylene glycol, diethylene glycol, and glycerin;halogenated hydrocarbons such as methylene chloride, 1,1-dichloroethane,1,2-dichloroethylene, 1-chloropropene, 1-chlorobutane, 1-chloropentane,chlorobenzene, bromobenzene, o-dichlorobenzene, and m-dichlorobenzene;amides such as N,N-dimethylformamide, and N,N-dimethylacetamide;pyrrolidones such as N-methylpyrrolidone; lactones such asγ-butyrolactone; sulfoxides such as dimethyl sulfoxide; saturatedhydrocarbons such as hexane, cyclohexane, and heptane; and other organicpolar solvents. Further, examples include aromatic hydrocarbons such asbenzene, toluene, and xylene, and other organic nonpolar solvents. Thesolvent can be used alone or in combination of two or more kinds. Also,in order to obtain an excellent pattern shape, the organic solvent andwater, or the basic or acid aqueous solution can be used in combinationas a mixed solvent.

From the viewpoint of the cost of the developer itself and productionequipments, and waste liquid treatment, development with the basicaqueous solution is preferable. Particularly, if high reliability isrequired for the polyimide film to be finally obtained, organic base ismore preferably used than a hydroxide of an alkali metal or an alkalineearth metal. Particularly, from the viewpoint of being easily availableand cost, tetramethylammonium hydroxide (TMAH) is preferable.

The development can be performed by any of known development methodssuch as spray development, dipping development and puddle development.The temperature upon development is preferably 1° C. to 80° C., morepreferably 4° C. to 60° C.

If necessary, rinse treatment may be performed after the development. Arinse may be appropriately selected from water, a mixture of water andthe organic solvent and the basic aqueous solution.

In the case of the positive type required to decrease the amount ofresidues in the film, and being hard to completely eliminate theprotective groups in the heating step for imidization hereinaftermentioned, though number of steps increases, a method including thefollowing steps may also be employed after development and patternformation: exposing the whole film or molded body followed by heating,if necessary, to eliminate the protective groups, and then, performingimidization hereinafter described.

After the developing step, imidization is performed. Generally, theimidization is often performed by heating in an oven or a hot plate.

Generally, it is said that imidization of polyamic acids graduallystarts from about 150° C., and mostly completes at around 200° C. ormore. However, if higher reliability is required, it is necessary toproceed closer to a complete imidization. In this case, heating at atemperature of Tg of the polyimide film to be finally obtained or higheris ideally performed. However, generally, a polyimide film havingreliability sufficient for practical use can be obtained by heating at300° C. to 400° C.

In the case of the resin composition of the present invention, it ispossible to accelerate the elimination of protective group-derivedresidual components closer to a complete elimination by extending theheating time at 180° C. or less since the hemiacetal ester bonddecomposes completely at around 180° C. Longer heating time ispreferable from the viewpoint of decreasing the amount of residualcomponents in the polyimide. Heating for 1 minute to 180 minutes, morepreferably 5 minutes to 120 minutes, in total at 40° C. or more and 180°C. or less is preferable in order to balance the decrease of the amountof residual components and productivity.

Further, in accordance with the intended use, heating at 180° C. to 450°C., preferably 200° C. to 400° C., may be performed, in order tocomplete imidization. Preferably, the highest heating temperature is251° C. or more and 400° C. or less.

Particularly, when heating is performed at 100° C. or more, it ispreferred to perform under inert atmosphere such as nitrogen or argon inorder to prevent oxidation of the polyimide and a substrate. Further, inorder to decrease the amount of residual components in the polyimide, itis preferred to perform under reduced pressure.

Particularly, heating conditions in the heating step in which the filmor molded body made of the photosensitive resin composition is heatedupon being formed or after being formed and before exposure, used forthe photosensitive resin composition containing the above-mentionedpolyimide precursor and the compound which generates a carboxylic acidby the action of light, may be determined, for example, by performing apreliminary experiment as follows.

Firstly, for example, the relationship between the heating conditionsand the rate of decomposition of hemiacetal ester bonds is obtained by:heating a 1 wt % deuterated DMSO solution of the polyimide precursor ina NMR tube, and determining the relationship from the integrated ratioof peaks of NMR spectrum; applying the solution of the polyimideprecursor on a substrate such as alkali-free glass having a thickness of800 λm, heating on a hot plate, preparing samples different intemperature and heating time, measuring the samples by IR, anddetermining the relationship from the integrated ratio of peaks derivedfrom vinyl ethers by IR spectrum; or dissolving the samples indeuterated DMSO, measuring the samples by NMR, and determining therelationship from the integrated ratio of spectrum.

From the relationship between the heating conditions and the rate ofdecomposition of hemiacetal ester bonds obtained as above, the range ofheating conditions is appropriately narrowed down. The dissolution rateof a sample prepared in the same condition as the heating conditions ofnarrowed-down range with respect to a developer is obtained. Then, theheating conditions (heating temperature, heating time and so on) can bedetermined in such a way that the rate of decomposition is within therange in which the dissolution rate of a film made of the polyimideprecursor being used alone is from 0.1 nm/s to 100 nm/s, preferably from0.5 nm/s to 50 nm/s, more preferably from 1 nm/s to 20 nm/s, withrespect to a developer.

Alternatively, there is a way not obtaining the rate of decomposition ofhemiacetal ester bonds. Specifically, a plurality of samples differentin heating temperature and heating time of a film made of the polyimideprecursor being used alone are formed. Then, the heating conditions maybe determined from a sample which has a dissolution rate of 0.1 nm/s to100 nm/s, preferably 0.5 nm/s to 50 nm/s, more preferably 1 nm/s to 20nm/s, with respect to a developer.

Also, particularly, in the case of the photosensitive resin compositioncontaining the compound which generates a carboxylic acid by the actionof light, and when required to decrease the amount of residues in thefilm or to improve transparency of the film, though number of stepsincreases, a method including the following steps may also be employedafter development and pattern formation: exposing the whole film ormolded body to generate carboxylic acids, and then, performingimidization. Particularly, if the compound which generates a carboxylicacid by the action of light is a compound having an o-quinone diazidegroup, the effect is high since changing into a carboxylic acid byexposure to photobleach improves transparency.

The photosensitive resin composition according to the present inventionis capable of pattern forming in such a manner that the surface of thefilm or molded body made of the composition is irradiate withelectromagnetic waves to selectively make an irradiated site easily orhardly soluble. Thus, it is possible to attain pattern forming bydevelopment without using a resist film for protecting the surface ofthe film or molded body made of the photosensitive resin compositionfrom a developer. The merit of this method is that processes of patternforming are simple. Particularly, the use of the basic aqueous solutionis small in environmental burden and adverse affect on industrialhealth.

IV. Article

The photosensitive resin composition of the present invention may beused in all known fields and products using resin materials such asprinting inks, adhesives, electronic materials, optical circuit parts,molding materials, resist materials, building materials,three-dimensional articles, and optical members. Since thephotosensitive resin composition of the present invention can selectpolyimide precursors of a wide range of structures so that functionsbeing characteristics of polyimides such as heat resistance, dimensionalstability, and insulation can be imparted to the cured product made ofthe resin composition, the resin composition is suitable for all knownfilms for members, coated films or three-dimensional structures in whichpolyimides are used. Particularly, the photosensitive resin compositioncontaining the polyimide precursor is mainly used as pattern-formingmaterials (resist). A pattern formed therewith functions as a permanentfilm made of the polyimide and as a component imparting heat resistanceand insulation.

The photosensitive resin composition of the present invention may besuitably used as a paint, a printing ink, an sealant, an adhesive, or aformation material of displays, semiconductor devices, electronic parts,micro electro mechanical systems (MEMS), optical members or buildingmaterials. Specifically, as for examples of the formation materials ofdisplays, the resin composition of the present invention can be used asa layer formation material and an image formation material for colorfilters, flexible display films, resist materials, and orientationlayers. Also, as for examples of the formation materials ofsemiconductor devices, the resin composition of the present inventioncan be used as a resist material, and a layer formation material usedfor buffer coating layers. Also, as for examples of the formationmaterials of electronic parts, the resin composition of the presentinvention can be used as an encapsulant and a layer formation materialfor printed circuit boards, layer insulation films, and wire coverfilms. Also, as for examples of the formation materials for opticalmembers, the resin composition of the present invention can be used asan optical material and a layer formation material for holograms,optical waveguides, optical circuits, optical circuit parts, andantireflection films. Also, as for examples of the building materials,the resin composition of the present invention can be used as a paint,and a coating agent. Also, the resin composition of the presentinvention may be used as a material for optical three-dimensionalobjects.

According to the present invention, an article selected from printedproducts, displays, semiconductor devices, electronic parts, opticalmembers and building materials, at least a part of which is formed withthe photosensitive resin composition of the present invention or a curedproduct thereof, is provided.

EXAMPLES Production Example 1

After a 100 ml three-neck flask was heated under nitrogen flow to bedried sufficiently, 0.99 g of a white solid substance of BPDA-ODA (apolyamic acid made of 3,3,4,4-biphenyltetracarboxylic dianhydride and4,4′-diaminodiphenyl ether; number average molecular weight obtainedfrom NMR of 12,000), which was obtained by polymerizing with adimethylacetamide solvent followed by refining by reprecipitation withacetone and drying a precipitate obtained, 5 g of n-butyl vinyl ether(n-BVE), and 5 ml of dried γ-butyrolactone were charged in the flaskwith careful attention to moisture in the air. Stirring was performedwith a magnetic stirrer for 112 hours under dried nitrogen flow at roomtemperature. BPDA-ODA did not dissolve in the beginning but dissolvedwith progression of the reaction, and became a brown liquid. Then, ahalf amount of the reaction liquid was reprecipitated with dried diethylether. Thus, a white solid substance of BPDA-ODA protected by n-butylvinyl ether (polyimide precursor 1) represented by the following formulawas quantitatively obtained. Through analysis of ¹H-NMR, it wasconfirmed that the protection rate (the reactivity of hemiacetal esterbonds to carboxyl groups) was 100% determined from a ratio of anintegral value of peaks of hydrogens bonded to the carbon betweenoxygens of hemiacetal ester bonds around 6.2 ppm to an integral value ofpeaks of hydrogens of aromatic rings of diphenyl ether.

Production Examples 2 to 5

Synthesis was performed in the similar conditions as Production example1 except that n-butyl vinyl ether was changed to different vinyl ethercompounds shown in Table 1. In all experiments, white solid substancesof polyimide precursors 2 to 5 having a protection rate of 100% wasobtained quantitatively without gelation. As for polyimide precursor 5,the ratio of protective groups of n-BVE and VEEA (n-BVE:VEEA) was 65:35from the integrated ratio obtained by 1H-NMR.

TABLE 1 Reaction Vinyl ether compound time Production PolyimideCyclohexyl CVE  88 hrs example 2 precursor 2 vinyl ether ProductionPolyimide t-Butyl vinyl t-BVE  48 hrs example 3 precursor 3 etherProduction Polyimide Ethylene glycol EGBVE 112 hrs example 4 precursor 4butyl vinyl ether Production Polyimide A mixed n-BVE:VEEA = 112 hrsexample 5 precursor 5 compound of 65:35 n-butyl vinyl ether and VEEA bymolar ratio of 65:35

Production Example 6

Synthesis was performed in the similar conditions as Production example1 except that 3,4-dihydro-2H-pyrane (DHP) was used instead of n-butylvinyl ether, and the reaction time was 240 hours. In the experiment,gelation did not occur, and a white solid substance of polyimideprecursor 6 was obtained. Similarly as Production example 1, throughanalysis of ¹H-NMR, it was confirmed that the protection rate (thereactivity of hemiacetal ester bonds to carboxyl groups) of Productionexample 6 was 100%.

Production Example 7

Synthesis was performed in the similar conditions as Production example1 except that 2-vinyloxy tetrahydropyrane (THPVE, a primary vinyl ethercompound) was used instead of n-butyl vinyl ether, and the reaction timewas 112 hours. In the experiment, gelation did not occur, and a whitesolid substance of polyimide precursor 7 was obtained. Similarly asProduction example 1, through analysis of ¹H-NMR, it was confirmed thatthe protection rate (the reactivity of hemiacetal ester bonds tocarboxyl groups) of Production example 7 was 100%.

Production Example 8

After a 100 ml three-neck flask was heated under nitrogen flow to bedried sufficiently, 1.98 g of a white solid substance of BPDA-ODA (apolyamic acid made of 3,3,4,4-biphenyltetracarboxylic dianhydride and4,4′-diaminodiphenyl ether), which was obtained by polymerizing with adimethylacetamide solvent followed by refining by reprecipitation withacetone and drying, 5 g of 2-vinyloxy tetrahydropyrane (THPVE), and 10ml of dried γ-butyrolactone were charged in the flask with carefulattention to moisture in the air. Stirring was performed with a magneticstirrer for 44 hours under dried nitrogen flow at room temperature.BPDA-ODA did not dissolve in the beginning but dissolved withprogression of the reaction, and became a brown liquid. Then, a part ofthe reaction liquid was reprecipitated with dried diethyl ether. Thus, awhite solid substance of BPDA-ODA partially protected by vinyl ether wasobtained. Through analysis of ¹H-NMR, it was confirmed that theprotection rate (the reactivity of hemiacetal ester bonds to carboxylgroups) was 55% determined from a ratio of an integral value of peaks ofhydrogens bonded to the carbon between oxygens of hemiacetal ester bondsaround 6.2 ppm to an integral value of peaks of hydrogens of aromaticrings of diphenyl ether. Furthermore, 5 g of cyclohexyl vinyl ether wasadded to the reaction liquid, and stirred at room temperature for 24hours. A part of the reaction liquid was reprecipitated with drieddiethyl ether. Thus, a white solid substance of polyimide precursor 8was obtained. In the similar procedures as Production example 1, aprotection rate and a molecular weight were measured. The protectionrate was 100% (CVE/THPVE=35 mol %/65 mol %). The weight averagemolecular weight in terms of the polystyrene calibrated standardmeasured by GPC was 18, 600. The reaction time was 68 hours.

Production Example 9

After a 100 ml three-neck flask was heated under nitrogen flow to bedried sufficiently, 1.98 g of a white solid substance of BPDA-ODA (apolyamic acid made of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and4,4′-diaminodiphenyl ether), which was obtained by polymerizing with adimethylacetamide solvent followed by refining by reprecipitation withacetone and drying, 5 g of 2-vinyloxytetrahydropyrane (THPVE), 5 g ofcyclohexyl vinyl ether (CVE), and 10 ml of dried γ-butyrolactone werecharged in the flask with careful attention to moisture in the air.Stirring was performed with a magnetic stirrer for 44 hours under driednitrogen flow at room temperature (25° C.). BPDA-ODA did not dissolve inthe beginning, but dissolved with progression of the reaction, andbecame a brown liquid. Then, apart of the reaction liquid wasreprecipitated with dried diethyl ether. Thus, a white solid substanceof BPDA-ODA protected by vinyl ether (polyimide precursor 9) wasobtained. Through analysis of ¹H-NMR, it was confirmed that theprotection rate (the reactivity of hemiacetal ester bonds to carboxylgroups) was 100% determined from a ratio of an integral value of peaksof hydrogens bonded to the carbon between oxygens of hemiacetal esterbonds around 6.2 ppm to an integral value of peaks of hydrogens ofaromatic rings of diphenyl ether. The ratio of protected substituents(CVE/THPVE) was 77 mol %/23 mol %. The weight average molecular weightin terms of the polystyrene calibrated standard measured by GPC was18,200.

Production Examples 10 to 11

Similarly as Production example 9 except that tert-butyl vinyl ether(t-BVE) was used instead of CVE, polyimide precursor 10 (t-BVE/THPVE=93mol %/7 mol %) was obtained. The reaction time was 40 hours, and theweight average molecular weight was 17,900.

Also, similarly as Production example 9 except that3,4-dihydro-2H-pyrane (DHP, a primary vinyl ether compound) was usedinstead of THPVE, polyimide precursor 11 (CVE/DHP=85 mol %/15 mol %) wasobtained. The reaction time was 70 hours, and the weight averagemolecular weight was 18,100.

Production Example 12

In the similar conditions as Production example 4 except that thepolyamic acid was changed to BPDA-4PPD-10DA (a polyamic acid synthesizedusing dianhydride (3,3′,4,4′-biphenyltetracarboxylic dianhydride) anddiamine (a mixture of paraphenylene diamine and 4,4′-diaminodiphenylether by molar ratio of 4:1); number average molecular weight by NMR of14,000), polyimide precursor 12 was synthesized.

Production Example 13

After a 200 ml three-neck flask was heated under nitrogen flow to bedried sufficiently and cooled to room temperature (25° C.), 5.88 g (20mmol) of 3,3′,4,4′-3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA),30 g of cyclohexyl vinyl ether (CVE), and 25 g of preliminarilydehydrated γ-butyrolactone were charged in the flask with carefulattention to moisture in the air. Stirring was performed under nitrogenflow at room temperature.

Therein, a liquid having 4.0 g (20 mmol) of 4,4′-diaminodiphenyl ether(ODA) dissolved in 20 g of preliminarily dehydrated γ-butyrolactone wasdropped gradually for 30 minutes. After completion of dropping, aprecipitate deposited. However, after the following stirring at roomtemperature, the precipitate was totally dissolved. Continuously,stirring was performed for 168 hours to complete the reaction.

A part of the liquid was refined by reprecipitation with dehydrateddiethyl ether. Thus, a white solid substance was obtained. A deuterateddimethyl sulfoxide solution of the white solid substance was analyzed by¹H-NMR. It was confirmed that the white solid substance was BPDA-ODA (apolyamic acid made of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and4,4′-diaminodiphenyl ether) in which all carboxyl groups were protectedby CVE. Through analysis of ¹H-NMR, it was confirmed that the protectionrate (the reactivity of hemiacetal ester bonds to carboxyl groups) was100% determined from a ratio of an integral value of peaks of hydrogensbonded to the carbon between oxygens of hemiacetal ester bonds around6.2 ppm to an integral value of peaks of hydrogens of aromatic rings ofdiphenyl ether. The number average molecular weight, determined from aratio of an integral value of peaks derived from end groups to anintegral value of peaks of diphenyl ether parts in repeating units in¹H-NMR spectrum, was 9,200 (polyimide precursor 13).

Production Example 14

Synthesis was performed in the similar conditions as Production example13 except that cyclohexyl vinyl ether was changed to ethylene glycolbutyl vinyl ether. Gelation did not occur. Thus, a white solid substanceof polyimide precursor 14 was obtained. The reaction time was 220 hours,and the number average molecular weight was 10,300.

Production Example 15

Synthesis was performed in the similar conditions as Production example13 except that cyclohexyl vinyl ether was changed to t-butyl vinylether. Gelation did not occur. Thus, a white solid substance ofpolyimide precursor 15 was obtained. The reaction time was 150 hours,and the number average molecular weight was 7,100.

Production Example 16

Synthesis was performed in the similar conditions as Production example1 except that n-butyl vinyl ether was changed to isopropyl vinyl ether.Gelation did not occur. Thus, a white solid substance of polyimideprecursor 16 was obtained. The reaction time was 88 hours. Similarly asProduction example 1, through analysis of ¹H-NMR, it was confirmed thatthe protection rate (the reactivity of hemiacetal ester bonds tocarboxyl groups) was 100%.

Production Example 17

Synthesis was performed in the similar conditions as Production example1 except that n-butyl vinyl ether was changed to sec-butyl vinyl ether.Gelation did not occur. Thus, a white solid substance of polyimideprecursor 17 was obtained. The reaction time was 88 hours. Similarly asProduction example 1, through analysis of ¹H-NMR, it was confirmed thatthe protection rate (the reactivity of hemiacetal ester bonds tocarboxyl groups) was 100%.

The half of reaction liquids of Production examples 1 to 17 remainedwere referred to as polyimide precursor resin compositions 1 to 17containing a polyimide precursor and a vinyl ether compound. No changesuch as gelation and production of precipitate was observed in thepolyimide precursor resin compositions 1 to 17 after storage at roomtemperature for 300 hours.

Comparative Production Example 1

Reaction was performed in the similar conditions as Production example 1except that vinyl ether being used was change to 5 g of VEEA(manufactured by Nippon Shokubai Co., Ltd.). As a result, the reactionliquid gelated after 200 hours.

Comparative Production Example 2

Reaction was performed in the similar conditions as Production example 1except that vinyl ether being used was changed to 5 g of a mixture ofVEEA (manufactured by Nippon Shokubai Co., Ltd.) and n-butyl vinyl etherby mole equivalent of 1:1. As a result, the reaction liquid gelatedafter 290 hours.

Reference Examples 1 to 6 Synthesis of Model Compounds

In the similar method as Production example 1, model compounds 1 to 6 ofthe following structures were synthesized. In all experiments, gelationdid not occur, and the protection rate of carboxyl groups was 100%.

<Storage Stability Evaluation of Polyimide Precursor>

As for a 2 wt % deuterated dimethyl sulfoxide solution (not dehydrated)of model compounds 1 to 6 obtained in the above production examples, therate of decomposition of hemiacetal ester bonds after storage at roomtemperature for 24 hours was measured. Similarly as Production example1, a protection rate was measured by 1H-NMR, and the rate ofdecomposition was determined from the following formula:

Rate of decomposition (%)=(1−protection rate after storage/protectionrate just after preparation)×100

TABLE 2 Relationship between the structure of hemiacetal ester bond andthe rate of decomposition after 24 hours Rate of decomposition ofhemiacetal ester bonds (%) Vinyl ether Dianhydride n-BVE CVE t-BVE ModelModel Model compound 1 compound 2 compound 3 PMDA 100 100 100 ModelModel Model compound 4 compound 5 compound 6 BPDA  56  80 100 PMDA:pyromellitic dianhydride BPDA: 3,3′,4,4′-biphenyltetracarboxylicdianhydride

Both PMDA and BPDA are representative dianhydrides used for polyimideshaving a low linear thermal expansion coefficient. The above resultsshow that, as for dianhydrides, hemiacetal ester bonds having higherstability can be formed by BPDA than PMDA. Further, vinyl ethercompounds used for protection were highly stable in the order oftertiary carbon<secondary carbon<primary carbon (vinyl ether compoundshaving lower rate of decomposition were more stable).

The above results show that PMDA series in the liquid was almostcompletely decomposed after 24 hours.

Similarly, as for a 2 wt % deuterated dimethyl sulfoxide solution (notdehydrated) of polyimide precursors 1 to 4 obtained in the aboveproduction examples, both rates of decomposition of hemiacetal esterbonds after storage at room temperature for 24 hours and 120 hours weremeasured. Similarly as Production example 1, the rate of decompositionwas determined by 1H-NMR from the integrated ratio of peaks.

TABLE 3 The structure of polyimide precursors and the rate ofdecomposition (%) after 24 hours and 120 hours Vinyl ether 24 hrs 120hrs Polyimide n-BVE 5 60 precursor 1 Polyimide CVE 68 100 precursor 2Polyimide t-BVE 100 100 precursor 3 Polyimide EGBVE 0 30 precursor 4

The influence of the structure of protective groups on storage stabilityin the polyimide precursors showed similar tendency as that in theexperiments of model compounds. Particularly, polyimide precursor 4,which has protective groups having an ether bond by a primary vinylether compound, exhibited excellent storage stability.

Also, it was confirmed that in comparison with model compounds,polyimide precursors having higher molecular weight have higherdecomposition stability.

<Thermal Decomposability Evaluation 1>

Using a 2 wt % deuterated dimethyl sulfoxide solution (not dehydrated)of polyimide precursors 1 to 4, 6, 7, 8 and 13, protection rates uponbeing heated were measured. After heating at each temperature for 5minutes in an NMR tube, similarly as Production example 1, theprotection rate was determined by 1H-NMR from an integrated ratio ofpeaks. The relationship between heating temperatures and protectionrates of polyimide precursor 2 and polyimide precursor 13, both usingcyclohexyl vinyl ether as a protective group, were the same. A graphrepresenting the relationship between the heating temperatures and theprotection rates of each polyimide precursor (polyimide precursors 1 to4, 6, 7 and 8) is shown in FIG. 1.

As shown in FIG. 1, thermal decomposability showed similar tendency asthe above-described storage stability. This results show that allhemiacetal ester bonds were broken in the liquid upon heating at about120° C. The protection rate of polyimide precursor 3 just afterpreparation was 100%. However, protective groups decomposed whilepreparing measurement of the protection rate, and the protection ratewas not 100% at room temperature upon starting the measurement.

<Stability Evaluation of Film Upon Heating>

Next, stability of actual film upon heating was confirmed using aninfrared spectrometer.

Reaction liquid 2 and reaction liquid 4 respectively upon synthesis ofpolyimide precursor 2 and polyimide precursor 4 were used as samples.Film having a thickness of 1 μm±0.1 μm were formed on a chrome-platedglass by coating. While raising the temperature from room temperature to150° C. at a rate of 5° C. per 1 minute on a hot plate, IR spectra weremeasured in real time.

Among the obtained spectra, peaks of 1,120 cm¹ derived from acetal partswere normalized for initial peak intensity as 100, peak intensities wereplotted with respect to temperatures. The plotted figure is shown inFIG. 2.

The peak intensities of both samples did not change at normalizedintensity of around 10 in a high-temperature region. It seems that therewas a baseline of spectrum in this portion, or a tail of an adjacentpeak overlapped this portion. Therefore, it can be assumed thatprotective groups were almost completely broken at around 110° C. inpolyimide precursor 2, and at around 150° C. in polyimide precursor 4.

Also, it can be considered that the normalized peak intensity graduallydecreased with continuous heating since the normalized peak overlappedthe peak of the vinyl ether compound remained in the film, and thereby,the intensity decreased with volatilization of the vinyl ether compoundfrom the film.

In comparison with the thermal decomposability evaluation of the liquid,in the evaluation of film, the decomposition temperature increased byabout 30 to 40° C.

From these results, it was confirmed that polyimide precursor 4particularly exhibits high stability with respect to heat in theprocesses of drying the film and so on.

As for condition when forming the film, while polyimide precursor 2slightly tended to be repellent to the substrate and had not so highadhesion to the substrate, polyimide precursor 4 was able provide a filmhaving a uniform thickness and had high adhesion to the substrate. Itcan be assumed that these results depend on the chemical structure of aprotective group. While the protective group of polyimide precursor 2 isa cyclohexyl group which has a bulky and high hydrophobic structure, theprotective group of polyimide precursor 4 is a butoxy ethyl group whichhas a flexible and hydrophilic structure. It can be considered that thispoint has influence on adhesion and film forming property.

<Thermogravimetric Decrease Evaluation>

The thermogravimetric loss of polyimide precursor 4 was measured byraising temperature by 10° C./min and providing nitrogen by 50 mL/min.

As a result, loss in weight at 300° C. was 41.9%, which is close to atheoretical value (41.5%) of loss in weight when elimination ofprotective groups and imidization completely proceed. It was confirmedthat the elimination reaction of protective groups and imidization werealmost completely proceeded. This suggests that decomposed products donot remain in the polyimide film, and there is no outgassing or declinein reliability when the polyimide precursor of the present invention isused.

<Infrared-Spectroscopic Evaluation>

Samples of polyimide precursor 4 and BPDA-ODA were respectivelysubjected to heat treatment under nitrogen atmosphere at 350° C. for onehour (heating rate of 10° C./min from room temperature). Then, theinfrared spectrum of each sample was measured. Though the baseline didnot slightly overlap, all main peaks were in the same wavenumber andboth spectra were almost the same. This showed that almost no impurityis remained in the polyimide precursor of the present invention afterimidization.

<Decomposability Evaluation when Base is Added>

cis-2,6-Dimethylpiperidine (DMP) was added as base to polyimideprecursor 2 and polyimide precursor 4 respectively. In the similarconditions as the thermal decomposability evaluation, decompositionbehaviors of polyimide precursor 2 and polyimide precursor 4 when baseis added were measured. A graph of the relationship between heatingtemperatures and protection rates of each polyimide precursor is shownin FIG. 3.

As a result, it was confirmed that the decomposition of polyimideprecursor 4 proceeds in the presence of base even at room temperature.Further, it can be understood that protective groups are almostcompletely eliminated at 60° C. in polyimide precursor 2, and at 30° C.in polyimide precursor 4. Since the protection rate can be changed bypresence or absence of base as above, the difference of solubility in adeveloper is assumed to be large, and it can be concluded that polyimideprecursor 2 and polyimide precursor 4 have sufficient patternformability.

<Decomposability Evaluation when Acid is Added>

p-Toluenesulfonic acid (p-Tos) was added as acid to polyimide precursor2 and polyimide precursor 4 respectively. In the similar conditions asthe thermal decomposability evaluation, decomposition behaviors ofpolyimide precursor 2 and polyimide precursor 4 when acid is added weremeasured. A graph of the relationship between heating temperatures andprotection rates of each polyimide precursor is shown in FIG. 4.

As a result, it was confirmed that decomposition proceeds in thepresence of acid even at room temperature. Further, it can be understoodthat protective groups of both samples are almost completely eliminatedat around 50 to 60° C. Since the protection rate can be changed bypresence or absence of acid as above, the difference of solubility in adeveloper is assumed to be large, and it can be concluded that polyimideprecursor 2 and polyimide precursor 4 have sufficient patternformability.

<Thermal Decomposability Evaluation 2>

Each of the reaction liquids of polyimide precursor 4 and polyimideprecursor 8 was applied on a chrome-plated glass by a spin coatingmethod, and dried by heating on a hot plate. Samples obtained therebywith different heating conditions were dissolved in deuterated DMSO, andmeasured by NMR to determine the protection rate of each sample. As aresult, when heating temperature increased and time passed, eliminationof protective groups proceeded, and the protection rate decreased. Therelationship between the heating temperature and the protection rate ofpolyimide precursor 4 is shown in FIG. 5, and the relationship betweenthe heating temperature and the protection rate of polyimide precursor 8is shown in FIG. 6.

<Dissolution Rate Evaluation of Polyimide Precursor>

In view of the results shown in FIGS. 5 and 6, the dissolution rate ofthe sample of polyimide precursor 4 of the heating condition with atemperature of 110° C. and a duration of 20 minutes, and the dissolutionrate of the sample of polyimide precursor 8 of the heating conditionwith a temperature of 100° C. and a duration of 10 minutes with respectto a 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueous solutionwere determined. The dissolution rate of polyimide precursor 4 was 4.3nm/s, and the dissolution rate of polyimide precursor 8 was 1.93 nm/s.

Example 1

20 wt % of an o-quinone diazide-based photosensitive agent (an ester of2,3,4,4′-tetrahydroxybenzophenone and6-diazo-5,6-dihydro-5-oxo-1-naphthalene sulfonic acid; product name:4NT-300; manufactured by Toyo Gosei Co., Ltd.) with respect to a solidcontent of polyimide precursor 4 was added to the reaction liquid ofpolyimide precursor 4 of Production example 4, and stirred. Thus,photosensitive resin composition 1 was prepared.

Example 2

30 wt % of an o-quinone diazide-based photosensitive agent (an ester of2,3,4-trihydroxybenzophenone and 6-diazo-5,6-dihydro-5-oxo-1-naphthalenesulfonic acid; product name: DTRP-250; manufactured by Daito ChemixCorporation) with respect to a solid content of polyimide precursor 8was added to the reaction liquid of polyimide precursor 8 of Productionexample 8, and stirred. Thus, photosensitive resin composition 2 wasprepared.

<Pattern Forming Evaluation 1 of Photosensitive Resin Composition(Positive Type)>

(1) Photosensitive resin composition 1 was applied on a chrome-platedglass by a spin coating method under the conditions below to form afilm. The film was subjected to after exposure at various exposuredoses, developed and rinsed.

Initial film thickness: 4.0 μm

Drying: 110° C. for 20 minutes

Development (dipping): a 2.38 wt % TMAH aqueous solution for 3 minutes(23° C.)

Rinse: H₂O for 5 seconds (23° C.)

A sensitivity curve under the above conditions was made to determinesensitivity. A positive type behavior, in which an exposed portiondissolves, was shown. The sensitivity was 110 mJ/cm².

The exposure was performed by means of a manual exposure equipment(product name: MA-1100; manufactured by Dainippon Screen Mfg. Co.,Ltd.). Light of a high-pressure mercury-vapor lamp was used withoutusing a filter.

Next, exposure was performed through a photomask, and pattern formingwas observed. Under the conditions below, a pattern with excellent shapewas obtained. The film thickness of pattern did not decrease even afterdevelopment. Further, heating was performed at 350° C. for 1 hour undernitrogen atmosphere to perform imidization. The film thickness was 2.6μm. The pattern did not lose shape and kept the state before baking.

Initial film thickness: 4.0 μm

Drying: 110° C. for 20 minutes

Exposure dose: 500 mJ/cm²

Development (dipping): a 2.38 wt % TMAH aqueous solution for 5 minutes(23° C.)

Rinse: H₂O for 5 seconds (23° C.)

Film thickness after development: 4.0 μm

The obtained pattern is shown in FIG. 7.

(2) Using photosensitive resin composition 2, a pattern formingevaluation was performed similarly as the above evaluation.

Initial film thickness: 4.3 μm

Drying: 100° C. for 10 minutes

Development (dipping): a 2.38 wt % TMAH aqueous solution for 5 minutes(23° C.)

Rinse: H₂O for 20 seconds (23° C.)

A sensitivity curve under the above conditions was made to determinesensitivity. A positive type behavior, in which an exposed portiondissolves, was shown. The sensitivity was 400 mJ/cm².

Next, exposure was performed through a photomask, and pattern formingwas observed. Under the conditions below, a pattern with excellent shapewas obtained. The film thickness of pattern did not decrease even afterdevelopment. Further, heating was performed under nitrogen atmosphere at350° C. for 1 hour to perform imidization. The film thickness was 2.5μm. The pattern did not lose shape and kept the state before baking.

Initial film thickness: 4.3 μm

Drying: 100° C. for 10 minutes

Exposure dose: 800 mJ/cm²

Development (dipping): a 2.38 wt % TMAH aqueous solution for 5 minutes(23° C.)

Rinse: H₂O for 20 seconds (23° C.)

Film thickness after development: 4.2 μm

The obtained pattern is shown in FIG. 8.

In view of the above results, since the rate of decomposition ofhemiacetal ester bonds can be controlled by the heating conditions ofthe polyimide precursor being used, the photosensitive resin compositionof the present invention can stably control the dissolution rate withrespect to the basic solution. Hence, in combination with a compoundwhich generates a carboxylic acid by the action of light such as any ofo-quinone diazide compounds, an excellent pattern can be formed.

Example 3

Using reaction liquid 4 of polyimide precursor 4, 14.25 parts by weightof polyimide precursor 4 (solid content), 39.5 parts by weight ofethylene glycol butyl vinyl ether (EGBVE), 45.5 parts by weight ofγ-butyrolactone, and 0.71 parts by weight (5 wt % of polyimide precursor4) of DNCDP (photobase generator) were mixed. Thus, photosensitive resincomposition 3 was obtained.

DNCDP has the following structure. DNCDP was synthesized by the methoddisclosed in Macromolecules, A. Mochizuki, Vol. 28, No. 1, 1995.

Example 4

Photosensitive resin composition 4 was prepared similarly as Example 3except that addition of 0.71 parts by weight (5 wt % of polyimideprecursor 4) of DNCDP (photobase generator) was changed to addition of1.42 parts by weight (10 wt % of polyimide precursor 4) of DNCDP.

Example 5

Photosensitive resin composition 5 was prepared similarly as Example 3except that addition of 0.71 parts by weight (5 wt % of polyimideprecursor 4) of DNCDP (photobase generator) was changed to addition of2.13 parts by weight (15 wt % of polyimide precursor 4) of DNCDP.

<Pattern Forming Evaluation 2 of Photosensitive Resin Composition>

Next, using photosensitive resin composition 3, pattern forming wasperformed under the conditions below. A microscope image afterdevelopment of pattern thereby obtained is shown in FIG. 9.

Initial film thickness: 0.9 μm

Drying: 80° C. for 10 minutes

Exposure dose: 70 mJ/cm²

Heating after exposure: 120° C. for 10 minutes

Development: a 2.38 wt % TMAH aqueous solution:isopropanol (IPA)=97:3(parts by weight) for 10 minutes (23° C.)

Rinse: a 3 wt % isopropanol aqueous solution for 15 seconds (23° C.)

As shown in FIG. 9, an excellent pattern was obtained at a resolution byline and space of 9 μm/9 μm. The pattern did not lose shape and kept thestate before baking even after imidization.

Further, after storing photosensitive resin composition 3 at roomtemperature for 120 hours, similar pattern forming ability wasexhibited. It can be assumed that since the reaction liquid was used inpreparation of photosensitive resin composition 3, protective groupsdecomposed by moisture were reproduced by vinyl ether in the reactionliquid.

From the aforementioned, it is clear that the photosensitive resincomposition of the present invention has high sensitivity andresolution, and exhibits high storage stability.

<Pattern Forming Evaluation 3 of Photosensitive Resin Composition>

Each of photosensitive resin compositions 3 to 5 were coated on achrome-plated glass, and dried on a hot plate at 80° C. for 10 minutes.Thus, films having a thickness of 3.5 μm were obtained. The films wereexposed in a pattern under the conditions below. Samples of the films ofphotosensitive resin compositions 3 and 4 formed on the chrome-platedglass different in heating temperature after exposure were formed, inwhich the temperature was changed from 80° C. to 150° C. by 10° C. atone time. Also, samples of the film of photosensitive resin composition5 formed on the chrome-plated glass different in heating temperatureafter exposure was formed, in which the temperature was changed from 90°C. to 120° C. by 10° C. at one time. The dissolution rates of an exposedportion and an unexposed portion of each sample were measured under theconditions below.

The obtained results are shown in Table 4 and FIG. 10.

Developer: a 2.38 wt % TMAH aqueous solution:IPA=95:5 (parts by weight)

Exposure dose in the exposed portion: 3,000 mJ/cm²

Condition of heating after exposure: heating at each temperature for 10minutes on a hot plate

Rinse condition: a 5 wt % isopropanol aqueous solution for 15 seconds

TABLE 4 Heating Dissolution rate (nm/s) temperature PhotosensitivePhotosensitive Photosensitive (° C.) after resin composition 3 resincomposition 4 resin composition 5 exposure Unexposed Exposed UnexposedExposed Unexposed Exposed 80 0.008 0.6 0.0007 0.5 90 0.008 0.6 0.00070.6 0.02 0.7 100 0.09 1.3 0.03 0.8 0.1 0.9 110 4.8 3.1 3.2 1.4 1.2 2.1120 45.3 13.1 109.5 12.9 41.8 2.6 130 82.3 66.3 90.9 16.5 140 45.5 49.365.5 9.4 150 11.5 6.6 7.9 2.7

The above results show that photosensitive resin compositions 3 to 5have a region at around 110° C. in which the dissolution rate of theunexposed portion exceeds the dissolution rate of the exposed portionunder the above-mentioned conditions of forming films by coating.Specifically, at temperatures lower than 110° C., the tendency of“positive type”, in which the dissolution rate of an exposed portion ishigher than that of an unexposed portion, was observed. At temperatureshigher than 110° C., the tendency of “negative type”, in which thedissolution rate of an unexposed portion is higher than that of anexposed portion, was observed.

The analyses of IR and NMR showed that when heating temperature afterexposure is less than 110° C., a slight amount of the hemiacetal esterbonds in the unexposed portion was thermally decomposed to givecarboxylic acids, but most of the parts remained as the hemiacetal esterbond. On the other hand, the hemiacetal ester bonds in the exposedportion decomposed due to the action of an amine generated from thephotobase generator, and a large amount of amic acids was produced.

In the case that the heating temperature after exposure was 120° C. ormore, most of the hemiacetal ester bonds in the unexposed portion werethermally decomposed and changed to carboxylic acids. On the other hand,elimination of the protective groups and imidization proceeded in theexposed portion due to the action of generated amines. It is assumedthat the amount of carboxyl groups in the polyimide precursor decreasedwhen imidization proceeded, so that solubility in a developer decreased,and thus the “negative type” behavior was observed.

<Pattern Forming Evaluation 4 of Photosensitive Resin Composition(Negative Type)>

Based on the results of Pattern forming evaluation 3, usingphotosensitive resin composition 5, a pattern forming evaluation wasperformed under the conditions below. Photosensitive resin composition 5was applied on a chrome-plated glass, and dried on a hot plate at 80° C.for 10 minutes. Thus, a film having a thickness of 3.5 μm was obtained.The surface of the obtained film was exposed in a predetermined patternunder the exposure conditions below. Heating after exposure wasperformed on a hot plate at 120° C. for 10 minutes. Development wasperformed under the development condition below. Thus, a pattern wasobtained. A microscope image of a pattern (negative image) obtainedthereby is shown in FIG. 11.

Film thickness after development: 2.4 μM

Exposure dose: 4,000 mJ/cm²

Developer: a 2.38 wt % TMAH aqueous solution:a 5 wt % IPA=100:5

Development time: 2 minutes

Rinse: a 5 wt % IPA aqueous solution for 15 seconds

<Pattern Forming Evaluation 5 of Photosensitive Resin Composition(Positive Type)>

In view of the result of Pattern forming evaluation 3, pattern formingevaluation was performed using photosensitive resin composition 5 underthe conditions below. Photosensitive resin composition 5 was applied ona chrome-plated glass, dried on a hot plate at 80° C. for 10 minutes.Thus, a film having a thickness of 1.5 μm was obtained. The surface ofthe obtained film was exposed in a predetermined pattern under theexposure conditions below. Heating after exposure was performed on a hotplate at 80° C. for 10 minutes. Development was performed under thedevelopment condition below. Thus, a pattern was obtained. A microscopeimage of a pattern (positive image) obtained thereby is shown in FIG.12.

Film thickness after development: 1.5 μm

Exposure dose: 2,000 mJ/cm²

Developer: a 2.38 wt % TMAH aqueous solution:a 5 wt % IPA 100:5

Development time: 40 minutes

Rinse: a 5 wt % IPA aqueous solution for 15 seconds

<Glass Transition Temperature after Imidization>

Photosensitive resin composition 3 was applied on UPILEX S 50S (productname, manufactured by Ube Industries, Ltd.) film attached on a glass,dried on a hot plate at 80° C. for 10 minutes, and peeled. Thus, a filmhaving a thickness of 20 μm was obtained.

Similarly, a 15 wt % NMP solution of BPDA-ODA was applied on UPILEX S50S (product name, manufactured by Ube Industries, Ltd.) film attachedon a glass, dried on a hot plate at 80° C. for 10 minutes, and peeled.Thus, a film having a thickness of 15 μm was obtained.

The above-mentioned two kinds of samples were irradiated with UV bymeans of aligner (light source: high-pressure mercury lamp) at 500mJ/cm² in terms of the wavelength calibrated by 365 nm, heated on a hotplate at 120° C. for 10 minutes, and then, heated at 350° C. for 1 hour(heating rate: 10° C./minutes) under nitrogen atmosphere. Films ofimidized products of photosensitive resin composition 1 (thickness: 12μm) and BPDA-ODA (thickness: 11 μm) were respectively obtained.

Dynamic viscoelasticity of each of the above films was measured by meansof a viscoelasticity analyzer (product name: Solid Analyzer RSA II;manufactured by Rheometric Scientific) at a frequency of 1 Hz and aheating rate of 5° C./min.

As a result, the glass transition temperature of the photosensitiveresin composition after imidization was 261° C., and that of theBPDA-ODA film was 258° C. It can be assumed that the difference is dueto presence or absence of a photobase generator contained.

<Linear Thermal Expansion Coefficient after Imidization>

The film formed for measuring the glass transition temperature ofphotosensitive resin composition 3 was cut into width of 5 mm and lengthof 20 mm, and used as an evaluation sample. Linear thermal expansioncoefficient was measured by means of a thermomechanical analyzer(product name: Thermo Plus TMA8310; manufactured by Rigaku Corporation).Measurement conditions were an observed length of evaluation sample of15 mm, a heating rate of 10° C./min, and a tensile load of 1 g/25,000μm², so that each load per area of cross section of evaluation sample isequal.

As a result, the linear thermal expansion coefficient of thephotosensitive resin composition after imidization was 42.5 ppm, andthat of the BPDA-ODA film was 43.9 ppm. It can be assumed that thedifference is due to the presence or absence of a photobase generatorcontained.

<Humidity Expansion Coefficient after Imidization>

The film formed for measuring the glass transition temperature ofphotosensitive resin composition 3 was cut into width of 5 mm and lengthof 20 mm, and used as an evaluation sample. Humidity expansioncoefficient was measured by means of a humidity variable mechanicalanalyzer (product name: modified Thermo Plus TMA8310; manufactured byRigaku Corporation). A difference between sample lengths of a samplebeing stable in an environment with a temperature of 25° C. and arelative humidity of 20% and the sample the relative humidity beingchanged to 50% and being stable was divided by a difference in humidity(in this case 50 minus 20 is 30). Then, the value obtained thereby wasdivided by the sample length at 20% RH. Thereby, the humidity expansioncoefficient was obtained. A tensile load was 1 g/25,000 μm² so that eachload per area of cross section of the evaluation sample was equal.

As a result, the humidity expansion coefficient of the photosensitiveresin composition after imidization was 21.5 ppm, and that of theBPDA-ODA film was 21.8 ppm. It can be assumed that the difference is dueto the presence or absence of a photobase generator contained.

Example 6

Using reaction liquid 2 of polyimide precursor 2, 11.3 parts by weightof polyimide precursor 2 (solid content), 43.2 parts by weight ofcyclohexyl vinyl ether (CVE), 45.5 parts by weight of γ-butyrolactone,and 0.57 parts by weight (5 wt % of polyimide precursor 2) of IrgacurePAG 103 (product name of a photoacid generator; manufactured by ChibaSpecialty Chemicals, Inc.) were mixed. Thus, photosensitive resincomposition 6 was obtained.

<Pattern Forming Evaluation 6 of Photosensitive Resin Composition>

Using photosensitive resin composition 6, a film was formed by coatingunder the conditions below, and subjected to exposure by variousexposure doses, heating after exposure, development, and rinse.

Initial film thickness: 1.6 μm

Drying: 50° C. for 10 minutes

Heating after exposure: 50° C. for 5 minutes

Development: a 2.38 wt % TMAH aqueous solution for 2 minutes (23° C.)

Rinse: H₂O:IPA=97:3 for 15 seconds (23° C.)

Using the film made of photosensitive resin composition 6, a sensitivitycurve was made by changing the exposure dose. The results are shown inFIG. 13.

As a result, a high sensitivity of 25 mJ/cm² was confirmed.

Next, using photosensitive resin composition 6, pattern forming wasperformed under the conditions below. Microscope images before and afterdevelopment of the pattern thereby obtained are shown in FIG. 14.

Film thickness: 1.6 μm (after development), 0.9 μm (after imidization)

Drying: 50° C. for 10 minutes

Exposure dose: 70 mJ/cm²

Heating after exposure: 50° C. for 5 minutes

Development: 2.38 wt % TMAH for 2 minutes (23° C.)

Rinse: H₂O:IPA=97:3 for 15 seconds (23° C.)

Imidization: 350° C. for 1 hour

As shown in FIG. 14, an excellent pattern was obtained at a highresolution by line and space of 4 μm/4 μm. The pattern kept the statewithout pattern crumbling and so on even after imidization.

Furthermore, even after storage at room temperature for 120 hours, thephotosensitive resin composition exhibited similar pattern formingability. It can be assumed that since the reaction liquid was used forpreparation of the photosensitive resin composition, the protectivegroups decomposed by moisture were reproduced by vinyl ether in thereaction liquid.

As aforementioned, it is clear that the photosensitive resin compositionof the present invention has high sensitivity and resolution, and showshigh storage stability.

1. A polyimide precursor having repeating units represented by thefollowing formula (1):

wherein R¹ is a tetravalent organic group; R² is a divalent organicgroup; R¹s may be the same or different from each other and R²s may bethe same or different from each other in the repeating units; R³ and R⁴each independently represent a monovalent organic group having astructure represented by the following formula (2) and may be the sameor different from each other; and R³s may be the same or different fromeach other and R⁴s may be the same or different from each other in therepeating units:

wherein R⁵, R⁶ and R⁷ each independently represent a hydrogen atom, ahalogen atom or a monovalent organic group; R⁸ is a monovalent organicgroup; R⁸s may be the same or different from each other in the repeatingunits; 35 mole % or less of R₈s are organic groups having a reactivegroup; and R⁵, R⁶, R⁷ and R⁸ may be bonded to each other to form a ringstructure.
 2. The polyimide precursor according to claim 1, wherein R⁸in the formula (2) comprises two or more kinds of organic groups.
 3. Apolyimide precursor resin composition comprising the polyimide precursordefined by claim 1 and a vinyl ether compound.
 4. The polyimideprecursor resin composition according to claim 3, which comprisessubstantially no acid material and basic material.
 5. A photosensitiveresin composition comprising the polyimide precursor defined by claim 1and a photoacid generator.
 6. A photosensitive resin compositioncomprising the polyimide precursor defined by claim 1 and a photobasegenerator.
 7. A pattern forming method comprising an exposure step ofirradiating a surface of a film or molded body of the photosensitiveresin composition defined by claim 5 or 6 with electromagnetic waves ina predetermined pattern, and a developing step of developing either anexposed or unexposed portion with a solvent which is capable ofdissolving the exposed or unexposed portion as a developer.
 8. Anarticle selected from the group consisting of a printed product, adisplay device, a semiconductor device, electronic parts, an opticalmember and a building material, at least a part of which article isformed of the polyimide resin composition defined by claim 5 or 6, or acured product thereof.